What Wears in derailleur chains is the inner link plates which have been punch forged to form less than half the width of the Roller .

the roller edges contact that and the inner surface of that partial Bushing will wear itself and the Pins ..

I suspect the Pins and rollers Are tempered differently than the chain link plates ..


The Pitch of all Bicycle Chains is 1/2" , 0.50" that is a standard ..

You want to Know the thickness of the Chains individual Centre pin it self ? remove one and measure it.

Wear per link may be to the 4th decimal Point (0.0001), but it all adds Up.