[Jedd]

Somewhere between 'ton' and 'tone'.

Though I think American English tends to pronounce 'ton' as 'tun', would that be right, or are there significant regional accent variations?

Anyway, refer sibling comments on common usage and cultural defaults - and I'll re-emphasize that it works really well for written communication. Like this.

[OJFord]

G'day - just to add for British English, here it's pronounced 'ton' (same as a ton) rhyming with 'stun' or TUN if you will.

It's extremely rare (don't think I've ever heard it) - except maybe in some industries still, I don't know - but there's an interesting history of advocacy/use of saying 'ton-E' or 'tunnie', to disambiguate the same way AmE pronounces it 'metric ton'.

[Jedd]

Aha, but are you from the south?

I've never heard it pronounced as a two-syllable word in the UK, but I confess to only very occasionally travelling north of Luton.

[OJFord]

SW, couldn't get much nearer the coast, yep.

I don't think it was ever common parlance, just important to disambiguate in some industries. Similarly I think 'thou' (-sandth of an inch) is preferred over 'mil' since that's such a common abbreviation of 'millimetre' (which =39thou, so you want to get that right).

[Jedd]

There was an article posted here a few months back on the subject of 'thousands of an inch', the misuse of 'mill', etc - and a slight digression around how our friends on the far side of the pond are fascinated by fractions.

https://news.ycombinator.com/item?id=34891145