A golf ball sized threaded foot roller ball! I have included a solid version and a halved version of the roller. The halved version can be used as a stand-alone massager or can be glued together to create a solid ball. Keep in mind the spikes on this ball are sharp, so sand them down to the desired height if this is too aggressive of a massage.
Pay attention to the support density chosen for this print. I used 15% and supports came off with a little bit more work than I hoped.