The Rover-Landers of BC

OK, so I was bored the other day and figured I would try to adjust my pump fueling down a bit as I was running a little hot.
So being a idiot I lost the white plastic ring shaped spacer that fits under the diaphragm and now I need to replace it.
so unless someone has a spare one lying around...
Can someone measure theirs for me (diameter and height) and I'll make up a new one on my friends lathe.
Also any advice on plastic type or is aluminum/copper/steel OK what do you think?

Thanks.
Glenn