Extra rubber washer in M/C kit

[53windsor]

 

This little guy at the top here. Andy Bernbaum kit. Everything else matches up with what I removed. What is it?

[kencombs]

Is the OD the same as the seal on the left, but only a different ID?   If so,I'd guess that it is included to make the kit fit multiple applications, maybe with different residual pressure valves.   Cheaper to do that than stock two different part numbers.

[Doug&Deb]

If all else fails call Bernbaums. I’ve found them to be very helpful any time I had a question.