[Joe Johnson]

If there is a "standard" bolt pattern in first it is the 6 screw pattern on the wheels, sprockets, hubs and such, specifically, 6 clearance holes for #10 screw (.196" or .200" depending on how much slop you are feeling that day) on a 1.875" bolt circle.

The hex hubs from AndyMark and VexPro both use that pattern. VexPro has additional torque transfer norkers (that's a technical term ;-) that fit into mating holes in there sprockets and wheels. They are really nice for some applications. They are overkill in others.

I typically don't use the VexPro norkers but sometimes I do. If I need more torque than I feel comfortable putting on the 6 bolts themselves, then I usually use a larger sprocket and put hole out farther on the sprocket to transfer the torque to the lever.

YMMV.

Dr. Joe J.