Hi Douglas,
The bolts that have bigger washers are designed to pull two objects together and hold them tight, and the washer spreads the load of them trying to pull apart over a larger area. A clevis pin, on the other hand, is only subjected to a shear load--the load is across it, not along it, so nothing is trying to pull it out. It only has a cotter pin or ring to prevent it from wiggling out from vibration, but the cotter bears no load at all, and thus has usually no washer whatsoever. Forespar may have used thin washers to keep the sharp ends of the cotter pin from scratching the toggle or whatever it is going through.
Best,
Ben
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