Nas1056 [2021] File

It seems you are referring to — likely a paper, standard, or document code.

A quick check of the NAS catalog shows that is not one of the most frequently cited standards (like NAS1835 for bolts or NAS1149 for washers). However, here is the most probable match: nas1056

Based on common aerospace and military specifications, stands for National Aerospace Standard (originally National Aircraft Standard). It seems you are referring to — likely