What washer? There's no washer. Be careful about using a wrench on the pivot bolt. That's the end of it you see in the picture above. If you apply too much torque, it will spin in the plate with the tab and you'll have no spring tension. It doesn't take much. I learned that the hard way. There's really no need to use a wrench at all. Just tighten the bolt from the backside. The pivot bolt won't turn because the tab stops it.

The pivot bolt is actually a nut in this application because the threads are female.