Summary

Insert.STL hold PCB and batteries
Hat.STL includes Lip to clip into body
Wheel.STL sized to fit O-Ring OD: 100mm CS: 6mm
Shims.STL sit between servo horn and thigh to provide a tighter fit
PipeStopper.STL sit on each end of the brass tubes

Instructions, PCB files etc at https://www.hackster.io/john-bradnam/robot-axis-red-c7bc45