Jay - According to the FAM the square steel washer is indeed for the front cab mount. From my perspective, the stack goes from bottom to top as the nut, lock washer, square washer, then any shims to get the specified "TOP OF FRAME TO BOTTOM OF FLOOR PANEL" dimension of 1.83" +.06 -.00.

The square washer prevent the lock washer from gouging into the rubber shims. wink
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Last edited by Gdads51; 04/11/2026 12:11 AM. Reason: add picture
~ Dan
1951 Chevy 3 window 3100
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"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)