5310-00-018-0351 (180351)
NSN 5310-00-018-0351 (NIIN 00-018-0351) is a lock washer in Federal Supply Class 5310, Nuts And Washers — a washer, usually round, with a centrally-located hole. Manufacturer part number 180351 (General Motors LLC, CAGE 7X677); also referenced as MILW6986TYPEA (Military Specifications).
NIIN assigned January 1963; DEMIL A (none required). Related NSN 5310-00-835-0574.