Summary

This is a remix of this original design:

https://www.thingiverse.com/thing:3912034

I remixed to fit the 6mm thick arms on a 7" source one. I left out the "crazy thick" version, because IMHO it's way too heavy. Even the "very_thin" version has 4mm deep counterbores, which is enough to protect the motor bolts I use, which have 3mm tall heads.

Supports are required. They work well printed with high durometer TPU (ie cheap/common tpu). If your printer can, I highly recommend printing them in nylon instead. Nylon is slightly heavier, but far more wear resistant and very slippery to help with grind/skid moves.