[petek]

I'll second Andy's rec for Delrin. This stuff is very strong, stable, easy to machine and gives a nice surface finish. Polyethylene (HDPE, UHMW, etc.) is good for high wear surfaces and for chemical resistance; I use it quite a bit in the lab. HDPE has pretty good stiffness, but is difficult to get really good dimensional stability and finish in machined parts. Tensile strength is much higher and more consistent with Delrin (70 MPa) than HDPE (15-40 MPa), too.

What that means for you is Delrin is about twice as strong, so you need half the thickness for a given load (saving weight and space) and you can tap threads in it with good load capability.

One thing to watch for with buying any material in stock size: the size tolerance is usually pretty loose. For the 1 x 1 bar stock Delrin, McMaster shows +.025" tolerance, meaning it may be anywhere from 1.000 to 1.025 thick. It is not uncommon to find wider tolerances than this in stock sizes.