The base code '20470' specifies universal head solid rivets. 'AD' indicates the rivet is made from 2117-T4 aluminum alloy. The '6' denotes a shank diameter of 6/32 inch (3/16 inch). The '7' denotes a shank length of 7/16 inch. The 'A' is a trailing variant code. While its specific meaning is not explicitly detailed in the provided sources, it is part of the full part number listed by distributors. MS is a specification number assigned by the United States Military Standard system. Governed by the MS standard series, administered by Military Standards.