[Retric]

I’ve never seen significant ware on a coin in circulation.

Have you?

[swores]

I have often, though I suspect not enough to make a significant difference to someone who is already OK with the slight variance between un-worn coins.

[seqizz]

I've seen enough wear to prevent them to be calibration material at least.

[MadnessASAP]

Depends on what your tolerances are. If you only need to be within a mm a coin is going to beat that by an order of magnitude.

We use a pack of cigarettes as a gauge for one of the jobs we do. Quick, (not so) cheap, and readily available. May have to standardize on a vape though in the near future.

[fanf2]

Only on counterfeit £1 coins, before the coins were redesigned to make them harder to fake

[xboxnolifes]

I have coins that originally had milled edges that are now completely smooth.