I measure chains with a 6-inch digital caliper; it reads to .01mm (accurate to .03). I measure 5.5 links because one jaw is too thick to fit between the narrower set of pins, 6.5 links is too long for the caliper. I measure different model chains as having different lengths new, as much as 1.5 mm out of 145. Do they have pins that are different thickness or have I mismeasured?

I thought for another minute and realized I'm not measuring the thickness of 12 pins, but only 2, unlikely to vary in thickness by as much as I measure.