Maybe we're talking about the various AF dimensions like found on "period" M8 and M10 nuts and bolts. For example a common industry standard M8 nut or bolt has a 13mm AF dimension, where most M8 nuts and bolts on "our" bikes are 12mm AF or sometimes 14mm AF.
Also the common M6 phillips head pan head screws have a larger head diameter compared to the period style.
OEM parts are normally correct but if you can find an aftermarket supplier who imports JAP standard screws, bolts and nuts, you're on a winner.