What is the maximum thickness of an 8/32 "washer" ?

Simple question. How thick can a washer be that’s still considered a washer?

I would say no more than 1/3 the diameter of the fastener. For 8-32 that’s about 1.5mm maximum.

For VRC purposes, I believe the washer just has to be ‘commercially available’ and needs to fit. So if you found a 1" thick ‘washer’, I guess its technically legal?

For non VRC purposes, the only definition I know of that defines how thick a washer can be are standards published by orginizations like ANSI, SAE, ISO, etc. That said, theres usually some company that doesn’t adhere to any standard.

So if I had a 5/16" OD 1/4" long plastic tube, is it a washer?

Is it sold as as a washer?

No… But if I slice it thin enough will it become one?

The definition of a washer is:

So if your purpose with a 1" thick “washer” is to spread pressure, relieve friction, or prevent leakage then it’s technically a washer. I think you may have some trouble explaining to an judge at inspection why you need a 1" thick washer however.