Richard,
I would think that would depend on what you can find
available,
PVC, plexiglas, 'Delrin', who knows what else. I've used a
multi-
layer thingy of plexiglas glued together before, seemed to work
okay. So the question is 'what can you find?'.
'Doc

I use the plastic from kitchen cutting boards for such parts. Strong and
easily available.

Torsten
N4OGW