Robert - It might be that you are just misreading the box info. Piston wrist pins are listed as GM Parts Group 0.636, a part identifier category, that has nothing to do with the actual diameter of the pins.
Your 1957 235 wrist pins came in standard, .0015 OS, .003 OS and .005 OS diameters. The basic standard diameter is 0.866" as noted by Kevin above. Below is a screenshot from a 1962 Chevy Master Parts Book showing the GM part numbers for each size pin.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
