what is this- a 67 part?

[cboss70]

Here is my mystery for today. I was cleaning up and found 2 large washers in with my 67 Shelby spares. Anyone know what there are used for- odd that they have a part number (ID54-200) on a washer so I figured I'd ask.

[2112]

Could it be for the post on the front seat hinge?

[shelbydoug]

It "resembles" the flat washers used on the "Comp seat belts".