This from Windline seems pretty good. What I really want to make sure is that I have a more or less standard size. So this gives me dimensions I can fabricate to, or no smaller than anyway. I can then either buy them or have something fabricated to the same size.
Hand cast from an elastomer unmatched in ability to resist wear and distortion at high loads
More durable, yet quieter than either hard plastic or metal
Hole Size: .5"
, the various diameters have different profiles. The 4" has a chain groove, but the 5" does not. Yet.