[jkqwzsoo]

In case anyone from the US reads this, BSPP and BSPT fittings are rare and incredibly frustrating here, as our NPT (National Pipe Taper) threads are different and the selection of BSP(P/T) fittings is extremely poor in comparison.

Also, I work with NPT fittings quite a lot:

> For what it’s worth, I tightly wrap the tape 10 times round the male thread and get an enraged mountain gorilla to tighten it up.

This is a WTF NO!!! for NPT and I’ll assume a WTF NO!!! for BSPT as well. You need about 1.5 wraps of PTFE tape to seal a fitting. Any more is wasteful and asking for leaks (or damage, if you’re using plastic fittings). It helps if you use the correct tape width for the fittings (1/4”, 1/2”, and 1” for me) and develop a wrapping method that keeps the tape under tension at all time and in such a direction that threading it into the fitting doesn’t unwrap the tape.

Also, in my experience, when someone inexperienced first learns what pipe tape is, they try to apply it to everything. 20 wraps around a tapered pipe? Wrap a Swagelok fitting? Try to make a butt joint or an adapter for two pieces of plastic tubing? I’ve seen it all.

[hilbert42]

"You need about 1.5 wraps of PTFE tape to seal a fitting. Any more is wasteful and asking for leaks"

I would have thought this obvious and it's essentially my experience (and I'm definitely not a plumber). However, I've found that more PTFE tape is needed on old or worn fittings or on ones that have damaged or badly cut threads—or when mating same sized pipes/fittings but each with different threads (yes, that's a desperate brute-force move in an emergency but I've had to force such matings on more than one occasion). In these circumstances, I'll use two or three turns or more often by trial and error—and this changes somewhat depending on whether I'm using thinner white PTFE tape or the thicker pink one.

Of course—not being plumber—it often happens that when I urgently need PTFE tape I cannot find it (it having been filed in some obscure place that I've forgotten about—even though I keep a reasonable stock of it), it's then I fall back to the good old combination of Hessian/burlap jute-type rope (of which there is always some lying around in my workshop) and linseed oil based paint. It's messy and much less convenient combination than PTFE tape but it still works wonderfully well. Moreover, it's more tolerant of the amount applied as the linseed oil actually binds to the pipe surface as opposed to the more 'mechanical' bond of the PTFE.

[jcims]

>Of course—not being plumber—it often happens that when I urgently need PTFE tape I cannot find it

Ahh, young padawan, the way of the elder is to buy a roll every time you have a project to do until you have achieved saturation...where there is a lightly used roll of teflon tape in every drawer and on every surface of your workshop and garage.

[hilbert42]

Ha! I'm no longer a Padawan so, like you, I'm well acquainted with the practice of spreading things around to the point of saturation.

It's not only PTFE tape that I spread around in copious quantities, other notables on the list are screwdrivers (of various sizes and types), superglue tubes (they go off with age anyway), propelling pencil leads, keys, USB and computer cables, USB pen drives, computer mice, adhesive tape, remote controls and any number of useful things.

The trouble is these supposedly inanimate objects come to life in the middle of the night and conspire not to be available when I most need them. Then the moment I've made do by jerry-built means they suddenly reappear! ;-)

[dtgriscom]

When I was a kid, my mom's theory on pencil purchasing was that if she bought enough, the house would be so saturated that you could shake a curtain and a pencil would fall out.

[hilbert42]

Hum... Clearly, I'm not alone. That's at least some comfort.

[geerlingguy]

Almost every night I pick up 3-5 pencils around the main living area at our house. Somehow there are always dozens of pencils around, but finding one with a working eraser on the end is as rare as finding a unicorn.

[semireg]

I just bought 24x 6” stainless steel rulers because every time I’d reach for one it’d be across the room at a different desk. Now I can capture a dozen at a time in their remote location for rehoming. Problem solved.

Also on my list of buy too many so I’m never left without: sharpies, microfiber cloths, jumper cables, rice (carbs), frozen sliced sourdough (fancy carbs), pocketable protein/energy bars.

[hilbert42]

I know, 12" rules are bad enough at disappearing but 6" ones seem as fleeting and ephemeral as the wind.

At least it's nice that one can now purchase them in packs of a dozen or so.

[bombela]

I am glad to be using metric. 150mm and 30cm rulers don't seems to run as fast as theirs us customary unit counterparts ;)

[hilbert42]

Mine are mainly metric or dual Imperial/metric too. I usually convert to Imperial because most readers are in the US.

If you were to read some of my old HN comments you'll realize defending the metric system in a US environment is pretty much a waste of time.

I recall one debate where some US commentators didn't have a clue about what a comfortable room temperature in Celsius would be. 68F=20C was meaningless to them even though 20C is a standard calibration temperature in lab and scientific work.

Not worth raising the issue.

[sokoloff]

I unlocked an uncommon DIY achievement last month: I finished an entire 119 foot roll of PTFE tape.

[fijiaarone]

All I have is Teflon tape, but I’ve never finished a roll. I think they sell them in only 3 feet sections now, but still the same spool size.

[hilbert42]

One has to ask 'finished it doing what'.

[bluGill]

Some sort of mummy costume party i'm sure

[jcims]

That’s beyond ’uncommon’, you should get a trophy.

[mindslight]

That's only the way of the middle-aged. If you do it with just PTFE tape you'll be fine, but if you do it with all similar sundries, then you'll be oversaturated and once again won't be able to find anything without pawing through piles.

[hilbert42]

Right, see my reply to jcims but that's not all of matter. One could suppose I'm going senile and perhaps that's true but the fact is that I've been losing stuff like this since before I was a teenager.

I've figured out the problem: my mind is thinking about all sorts of seemingly important stuff all the time but which in fact is mostly garbage, so my subconscious mind handles what my conscious mind consideres as procedural or unimportant. As my conscious and subconscious minds aren't on speaking terms sufficient for my liking I often end up with the problem of lost stuff.

If I consciously tell myself where I've put something then I very rarely forget where it is. The trouble is I don't remind myself to make note often enough.

[mindslight]

My own working model is one of complexity building up over time. You can handle it fine as long as you don't have many fields of endeavor, you have plenty of time to periodically focus on them, keep the stuff organized, can fully finish a project and button it up, etc. But then things happen where you're forced to clear out your mental cache, or even screw up your organization/storage system for whatever, and it comes crashing down. Then all the complexity you were managing gets in your way, and the problem snowballs unless you regain some bandwidth and take steps to mitigate the decay.

[hilbert42]

Right, that makes sense. And my explanation is more complex than I could detail in my comment.

I know I have too many diverse interests—fields of endeavor to quote you—and the older I get the more of them I accumulate. On the one hand having many interests is very useful because it allows me to see and understand common ideas or threads across quite disparate and diverse subjects that otherwise would not have been obvious but the matter of administration becomes a significant problem. Often I've little time to deal with prosaic matters so the mundane is often left to itself (disorder accumulates).

That said, I'm instinctively an orderly and tidy person, as I like to say 'there's a place for everything and everything in its place'. I hate mess and disorder but that doesn't mean that I don't experience it—I do so often for reasons that you mention. However, when entropy/disorder around me reaches a certain 'sensibility' threshold I'm triggered to have an almighty cleanup much to the chagrin of others around who have a more relaxed view of disorder.

Nevertheless, I'm not obsessive about it, sometimes I amaze myself at the level of disorder I'll tolerate. (Reordering things is boring and distracts me from my interests despite the fact that I'm competent and thorough about it. Essentially, the more preoccupied I am with something the higher my toleration for mess and disorder becomes).

[TeMPOraL]

Or you find yourself married and with children, and that final step of regaining some bandwidth becomes structurally impossible to achieve.

[andylynch]

This is the way. It’s also cheap enough that buying a dozen rolls upfront is less effort!

[SaintGhurka]

"combination of Hessian/burlap jute-type rope (of which there is always some lying around in my workshop) and linseed oil based paint."

Could you explain that? How do you seal pipe fittings with rope?

Edit: found an explanation. TIL that you can use the fibers just like tape and wrap the threads.

[hilbert42]

Perhaps if I'd used the proper name what I said may have been clearer. The correct name is hemp rope or plumber's rope but I don't often have that around (not being a plumber) so I use the next best thing available Hessian fabric or its rope equivalent).

Here are some photos: https://www.bunnings.com.au/enduraseal-1m-plumbers-hemp_p012...

https://waropes.com.au/twines/plumbers-hemp/

You wrap the hemp fibers around the threads that have been brushed with linseed oil paint then apply a little more paint to the hemp and then mate the couplings together. This sealing technique has been around at least for several hundred years if not longer.

[ethbr0]

>> [...] has been specifically designed and manufactured to suit the Australian market and conditions.

That's some hearty stuff, then!

[hilbert42]

First class BS if you ask me. Hardly anything could be more generic than hemp rope methinks.

[Sophistifunk]

That seems hella useful, I'm going to grab some next time I'm down picking up a snag sanga.

[throwaway294566]

You don't need oil, just rope works as well. Every DIY store (at least over here) has loose manila fibre for that purpose. Wrap into the thread, screw it together, done. The not-so-nice problem: It might leak at first. The nice feature: The fibres will soak up water (thats why oil is actually counterproductive), swell up and make a tight fit after half an hour or so. You can even readjust the angle (other than with PTFE tape), it'll just drip for another half hour.

[hilbert42]

Right, there are multiple variations but they generally work in skilled hands although I learned from plumbers who always used oil (although using oil was always an imperative with gas pipes). Using oil usually negates the initial leaking whilst waiting for the hemp to dampen and swell.

Edit: I agree that using oil is counterproductive with water pipes—initially at least. I was taught by both plumbers and my father (who wasn't a plumber but a mechanical engineer who worked on power station boilers) that using oil is better in the long run as it prevents the hemp from rotting and thus premature failure of the seal. Moreover, using one oil-based method means that a plumber cannot get confused and leave oil off gas connections where it's essential.

(I'd add that when referring to oil I'm specifically referring to linseed oil (even though I've seen some plumbers inappropriately use engine oil) because it slowly polymerizes and hardens even in the absence of air. This adds to the seal's effectiveness and further protects the hemp.)

[mgarfias]

A small quibble: the tape don’t seal. It’s a lubricant for the threads wedging together to seal.

For a REALLY good primer on the subject, read Carrol Smith’s _Nuts, Bolts, Fasteners and Plumbing Handbook_ (aka Screw to Win).

[kortex]

> the tape don’t seal.

No, the tape absolutely contributes to the seal. Sure, the lubrication lets you thread more tightly without binding, but that's not to say the tape isn't contributing to the seal. If it didn't, you would still have a spiral leakage path. PTFE tape is soft enough that it deforms and prevents the spiral leakage path which can occur with any tapered threaded joint.

I've actually used PTFE tape in super high pressure situations (>1000 psi) with straight (un-tapered) joints (you aren't typically supposed to, but this was for an experiment), and it indeed sealed.

> The tape also works as a deformable filler and thread lubricant, helping to seal the joint without hardening or making it more difficult to tighten

https://en.wikipedia.org/wiki/Thread_seal_tape

[lazide]

The tape is so incredibly soft, it isn’t doing much on that front.

You also don’t actually have a spiral leakage pattern with NPT if tightened appropriately- the fitting it self deforms to seal it.

You need the tape or some other dope so the metal doesn’t gall when you do it.

If you aren’t tightening it that tight, then yeah you’ll need rope or whatever.

If you pull apart the fitting afterwards, it’ll be really clear you only end up with a tiny, nearly molecule thin layer of the PTFE at the inside of the fitting, if anything.

[blincoln]

> You also don’t actually have a spiral leakage pattern with NPT if tightened appropriately- the fitting it self deforms to seal it.

This contradicts every source I've read about NPT threads, e.g.

"NPT pipe thread design allows slight clearance between the thread crests and mating roots. This clearance creates a spiral leak path along the male thread crests. The spiral leak path is why NPT connections require a thread sealant to be leakproof."

https://www.industrialspec.com/about-us/blog/detail/npt-nptf...

"NPT, or National Pipe Thread (Taper) is an American standard for pipe connection dating back to the middle of the 1800s [...] they require a thread sealant, such as PTFE tape, to fill the spiral leak path inherent to the fitting;"

https://www.fluidpowerworld.com/why-is-leakage-still-a-probl...

Thoughts?

[lazide]

Check out:

[https://www.ralstoninst.com/npt-female-quick-test-adapters]

“They seal due to the "out of roundness principle" which means that the male stretches the female fitting until there is so much force that the connection can hold pressure. One of the challenges with this design is that if you connect stainless steel to stainless steel then over-tightening or poor lubrication can cause gauling and damage to the threads. Thread sealant is needed to seal but only 2 turns of thread sealant is required. ”

And [https://brennaninc.com/brennan-university-old/fittings-101-n...]

“ NPT connections rely on thread deformation- a metal to metal sealing design where the threads of the connectors themselves form together. This design is ideal for single assembly applications and not recommended where connections will be assembled and disassembled frequently due to wear on the threads from deformation.”

I think you’re running across SEO spam. The bane of the internet. However, it is really commonly misunderstood, and I’ve heard all sorts of folks repeat it.

The thread sealant is to lubricate, and can help slightly in low pressure scenarios (like typical gas which is about 1/2PSI or 10-12 WC inches), but it’s to allow the fitting to work, not the primary sealing mechanism.

It’s not hard to do some back of the envelope calculations either and see that has to be true in many situations because the yield strength of PTFE tape or thread sealant (even when cured) is so low. It can’t hold on 100 PSI if it was what was doing the sealing.

Brass, Iron, Stainless? Piece of cake.

That said, there are thread sealants that do indeed provide high strength gas tight seals, loctite makes one for sure.

But it shouldn’t be necessary and isn’t generally in the plumbing aisle.

You can test out the lubrication effect yourself. It’s really obvious in brass, black iron, galvanized, and stainless fittings.

The standard ‘torque guidance’ for NPT fittings, is tighten to hand-tight, then do 2-3 turns.

Try it first without anything (with fittings you won’t mind losing), and the galling and friction is terrible. Often it’s impossible to do 2-3 turns, and hence it will leak. All the force is taken up with the friction on the threads. It may be impossible to undo due to the galling/cold welding.

Lubricating Oil on the threads? No issues, and you can tighten with no leaks unless the fitting is damaged or messed up.

Use tape or pipe dope? Usually even better than the lubricating oil, and minor damage won’t cause nuisance leaks which may require too much force otherwise.

Thin brass fittings and stainless steel are especially bad without some kind of lubricant. The brass even makes a shrieking sound, and is susceptible to cracking.

[johnwalkr]

Such a great book. I’m a mechanical/aerospace engineer and it’s astounding how many in my field don’t understand fasteners and tend to oversize them. It’s seen as conservative but it can actually backfire.

[pengaru]

> For a REALLY good primer on the subject, read Carrol Smith’s _Nuts, Bolts, Fasteners and Plumbing Handbook_ (aka Screw to Win).

+1 for anything by Carrol Smith

Back in my gearhead days Engineer To Win was a near constant fixture next to the toilet.

[mgarfias]

I had no idea he lived nearby when I was in HS (also Gurney’s shop was within biking distance, also didn’t know it).

If I could go back I’d blow off all the dumb shit I did and go ask to push a broom all day just to hang around race cars and learn.

[kennend3]

As someone who is NOT a pipe fitter but lived with one for many years.. It was odd reading this and I'm glad someone like you responded to correct things.

> For what it’s worth, I tightly wrap the tape 10 times round the male thread and get an enraged mountain gorilla to tighten it up.

Again, not a pipe fitter but this just screams "WRONG". If someone needs to use that much force to tighten it up, one can only assume that the pipe is now so full of tape it simply doesn't fit?

My roommate had a "unlimited BTU" gas fitter license (Canada Class "A") and this for a living and preferred "pipe dope"

"Pipe dope is generally stronger seal than Teflon tape, which is why plumbers and other professionals use it rather than tape for seals that are permanent."

[rsync]

"My roommate had a "unlimited BTU" gas fitter license (Canada Class "A") and this for a living and preferred "pipe dope""

I do this kind of thing a lot as we own and maintain our own water plant. My preferred sealant is the yellow PTFE tape that is used for natural gas.

It is quite a bit thicker than the white tape, it sticks to threads better and it is easier to work with, in terms of manual dexterity.

I never use the white tape for anything.

I don't like pipe dope at all and I only use it for large fittings that are going to be buried or inaccessible.

ALSO, helpful hint: If you are mixing plastic pipe (like schedule 40/80) and metal pipe, always have metal female couplings and plastic male couplings. A metal male going into a plastic female is one tighten away from cracking the plastic.

[amluto]

> ALSO, helpful hint: If you are mixing plastic pipe (like schedule 40/80) and metal pipe, always have metal female couplings and plastic male couplings. A metal male going into a plastic female is one tighten away from cracking the plastic.

Or buy transition fittings or "special reinforced" fittings. Or, if you trust them, use push-to-connect fittings -- SharkBite, John Guest, ProLock, etc. (ProLock appears to be a John Guest product that is also sold by SharkBite.)

I've seen plenty of female plastic threaded fittings break even when connected to male plastic threaded fittings. They're just not that strong under circumferential tension.

[jkqwzsoo]

The color isn’t necessarily related to the tape density. I always use Merco Threadmaster M66 (I think this, or the M77, is the McMaster default for high-density tape), which comes in all colors. I’ve had cheap tape come prepackaged with products that’s almost transparent and not with bothering with.

I also find it really helps to use the right tape width for the fitting you’re working with. I work mostly on small laboratory/pilot scale stuff (that needs to come apart in a few years, so no dope). I rarely use a fitting larger than 1/2”, but when I do, it’s a pain to use 1/2” tape. 1” (or 1.5”) will make a much neater and more consistent job. Similarly, I prefer 1/4” tape for 1/8” and smaller fittings.

[dsfyu404ed]

>ALSO, helpful hint: If you are mixing plastic pipe (like schedule 40/80) and metal pipe, always have metal female couplings and plastic male couplings. A metal male going into a plastic female is one tighten away from cracking the plastic.

At some point it becomes easier to just think about what you're doing avoid being ham fisted moron than it is to seek out parts and design things to be accommodating to that kind of behavior.

[couchand]

I've seen people suggest that white tape should only be 1.5-2 but yellow should be 5 or more, do you have thoughts on that? Is there a difference in usage or is it the same overuse pattern on both?

[rsync]

I have no idea.

I don't think you can use too much tape. Suggestions that you can break fittings with too much tape are almost certainly incorrect - with either plastic or metal.

I usually do 5-ish wraps with the thick yellow tape - and that is true with schedule 40 PVC, plain old galvy, or with small stainless fittings.

I am wasting tape, and I know it, and I have no problem with that - and neither do the fittings.

[jkqwzsoo]

You can definitely break a plastic fitting with too much tape. The tape and the plastic are deformable, and I’ve had taped PVC fittings effectively extruded by repeated installation with fresh tape (every time you install it, you need a little bit more). This effect will be amplified if you’re fitting is made out of a material more prone to creep like PVDF, PP, or Nylon. Granted, this isn’t a typical (or appropriate) use case, but it was a necessary kludge for a project I had.

You can get leaks with too much tape if it prevents you from reasonably getting the threads to seal. When this happens, you get a slow leak between the layers of the tape. I’ve seen water slowly bead out of fittings at 1000 psi due to this.

Also, too much tape can lead to contamination (the tape sticks to every piece of dust, lint, and oil in your workspace) and can make it easy to cross thread fittings (especially small plastic ones).

[dsfyu404ed]

>"Pipe dope is generally stronger seal than Teflon tape, which is why plumbers and other professionals use it rather than tape for seals that are permanent."

They use it because it's faster. As long as it's good enough any performance difference is secondary.

[aidos]

I think there’s cultural difference where the tongue in cheek context has been lost a bit.

They probably use neither 10 full wraps, nor an enraged mountain gorilla, but then I’ve seen stranger things in plumbing.

[quietbritishjim]

Except in the next sentence he says that he doesn't really use a gorilla (and that's the bit that's obviously a joke). But he doesn't say he doesn't use 10 wraps.

[lazide]

It’s hard to tell the difference between a frustrated home owner/part time plumber and an enraged silver back I guess.

At least one of them is vegetarian?

[naich]

In this case, both. Sorry.

[fuzzfactor]

The lowland gorilla comes to mind . . .

[mannykannot]

What do you think of the advice that it is acceptable to use a tapered male thread in a straight female one? My guess is that if you do that, you have at best one turn of the thread helix holding them together and providing a seal (and perhaps you would be trusting in nothing more than the tape jammed between the threads if you used ten turns of it!)

[johnwalkr]

I don’t think it’s acceptable. Maybe works in pinch to get through a weekend but I would always replace it with a proper fitting. Plus if you damage the female threads or o-ring seat, you’ve made a much worse problem for yourself.

[ethbr0]

It's probably a commentary on the idea that the tapered male diameter is its max diameter(?), versus straight is throughout.

Consequently, a tapered male will fully screw into a straight female, albeit with gaps between the threads at the deep end of the socket.

Whereas a straight male will at most only screw the first few threads into a tapered female, leaving most of the male hanging out.

[johnwalkr]

Tapered pipe threads are actually much larger than you’d expect given the nominal diameter. 1/4 inch tapered pipe threads have a maximum outer diameter of more than 1/2 inch and 18 threads per inch. They will sort of work with a 1/4 inch straight thread but not by fully screwing in.

[lazide]

It’s asking to rip the threads out of the fitting (and have done so when trying). One way you’ll get some seal first, the other you won’t.

[balls187]

> Also, in my experience, when someone inexperienced first learns what pipe tape is, they try to apply it to everything.

That’s me. Whoops.

[VLM]

Tape causes massive contamination problems with fuel and hydraulic systems.

Its not that the Teflon reacts with hyd oil, its that the inevitably little tiny bits of stuff physically jam/ruin seals and clog nozzles.

[culopatin]

But only if you put the tape over the edge. I usually leave the first 2 threads uncovered, why would it fall into the stream if you don’t cover the tip of the thread with it?

[VLM]

The most installed/removed NPT thread will leak the most thus have the most tape added and the scraping of installation/removal will guarantee teflon contamination of the system eventually.

You are also correct in that something installed one time for the lifetime of the system, especially with some care and attention to cleanliness, is almost certainly OK.

[kevin_thibedeau]

When you open up the joint, bits are left behind in the female half. Then they get pushed in when it's resealed.

[lazide]

The tip of the thread in NPT is the one that needs the lubrication the most, hah.

Pipe Dope causes similar issues though.

[rdl]

Ugh, I applied it to PVC pipe, which made it leak, sigh.

[VincentEvans]

There’s no problem applying it to a threaded connection in PVC. Unless you mean that you’ve figured out a way to apply to a fitting that’s meant to be glued? In that case I commend your abundant creativity.

[rdl]

My experience is that even one wrap of PTFE tape on threaded PVC causes it to loosen and then leak, and it's recommended by youtube/google to not use it. (Some say sealant is ok).

[hattmall]

The real pro-tip is not to use tape at all. Instead use pipe dope or joint compound, it's cheap, easy, and better in every possible way. If you only have two do one or two very low importance joints, like a showerhead then tape is fine. But for anything serious use the joint compound. If you are doing a lot of work it's absolutely a game changer.

[bdowling]

> This is a WTF NO!!!

I’m pretty sure the author was exaggerating, because no sane person would use an enraged gorilla to tighten fittings. Gorillas are simply far too dangerous to be trusted with important plumbing work.

[klyrs]

If you think plumbers are expensive, you've never tried to hire a gorilla for an hour.

[robk]

This is more useful than Teflon tape I find https://www.amazon.co.uk/Loctite-K97870-Henkel-Sealing-Multi...

[jve]

Thanks for mentioning this. This is so easy and fast to work with and you usually end up with sealed joints (Sorry, I'm an amateurish DIYer, first tries were failing). No additional grease needed to reduce friction, withstands high temps, for water and gas. What's not to love? Price maybe.

[shellfishgene]

In Germany using hemp fibers instead of the PTFE tape is still really common (together with a sealing paste calle Neo-Fermit). The disadvantage of the tape is that you can't turn the fitting backwards even a little bit when tightening it, or you get leaks. With hemp that does not matter so much as it swells up with water.

[azalemeth]

I particularly hate the confusion that BSP and NPT cause. They're almost interchangeable (differing, iirc, probably on the angle of flank) and will get about three turns in and then leak or fail under pressure. In my world, this has led to graduate students spraying liquid nitrogen around. It's clearly the case that the two probably were supposed to be identical but diverted due to manufacturing differences in the distant past.

The standard advice I've been given when it comes to either vacuum or cryo fittings is "cut anything American off it as soon as it arrives and put DIN standard or KF kit on as soon as possible". Standards are a pain and that xkcd about there being too many of them is very, very true.

[iancmceachern]

Little nit pick. BSP is British.

[dsfyu404ed]

Your comment reeks to high heaven of textbook engineer. The practices you advise do not survive in a world of bottom dollar commodity pipe fittings.

Everyone with dirty fingernails knows that 3-4 wraps is a pretty good rule of thumb for fittings that are meant to go together and you need more when you're mix and matching BSP and NPT threads because you have a larger leak path to take up.

Nobody bothers stocking multiple widths of tape. That only makes sense in a production environment where you're only ever working with one size and can build to it.

In a pinch you can "augment" things like compression fittings with tape on the OD of the ferrule.

[kortex]

> You need about 1.5 wraps of PTFE tape to seal a fitting.

Not a pipe fitter, but I've done a lot of plumbing on a huge variety of systems (sinks, drains, air lines, HPLCs and other chemistry equipment, bioreactors, RO systems, potato cannons). I have found through experience that the thick PTFE tape (usually grey or yellow) is almost always superior to the thin tape. I use 2-3 wraps of that and that seems to be ideal.

Thick tape is also a lot easier to remove than the thin PTFE if you have to reinstall (you aren't supposed to re-use tape if you unscrew it).

[berjin]

If you want a really good seal you wrap the tape 1-2 overlaps at the start of the thread and progressively make it thicker and thicker so you have more overlaps (10x) at the base. I guess it depends on the fittings but some run out of tapper and you can't tighten it anymore without the hexagonal nut hitting the adjacent fitting. This works well as you're building your own tapper which is sort of acting as an o-ring.

Generally BSP male fittings are always tapped which is why they don't mention it.

[jakewins]

Do you have a reference for this? Everything I've read is the purpose of the tape is to reduce friction (hence PTFE), not to actually seal. In other words, the seal comes from the fittings connecting tightly, made possible by 2-3 wraps of PTFE low friction tape.

[berjin]

A reference? This is plumbing not academia. The parts I get might be slightly different than the spec so you have to make up for it with the right amount of tape in situ. If you tighten the threads as much as possible and there is still a gap then you have to seal it somehow. Soft plastics will deform enough to seal without any tape at all but harder materials need something between to fill in the gaps.

[XorNot]

PTFE tape is meant to block the helical path around the screw threads for leaks to propagate. For parallel threads it's absolutely vital.

Taper threads are designed to crush together to achieve something similar, but for what's available at the hardware store I've always had problems.

[lazide]

That is a common falsehood.

Parallel threads need an alternative sealing method, or they’ll leak. If low pressure, dope or tape might be enough, but it’s using the fitting wrong.

Usually there is a flare, mating surface, or o-ring type setup that should be used instead. Examples would be welding tank connections, or scuba tanks that are at thousands of PSI.

For NPT, if the fitting is properly tightened, the fitting deforms and the threads mash together. They won’t leak even at hundred of PSI.

[TheJoeMan]

> when someone inexperienced first learns what pipe tape is, they try to apply it to everything

I just removed some from a medical oxygen DISS fitting, which is a conical seat on the inside meaning the threads do 0 sealing duh-oh.

[sokoloff]

I use a minimum of 4 wraps and usually 5 or 6 wraps on black pipe in the 3/4”-2” range. 2 wraps might be enough for nice clean plastic or brass threads in the 1/2” or less range, but larger steel fittings need more PTFE tape.

[PaulDavisThe1st]

Pipe dope FTW.

[jnellis]

Indeed. If your threads are new you're not supposed to use any teflon tape, you use pipe dope. Teflon tape is for worn threads when you are out of pipe dope.