Multi-use gear cutter arbor. By Clickspring. 3:16 video:
https://www.youtube.com/watch?v=GeNsqkyV52I
Previously:
https://www.homemadetools.net/forum/...593#post182268
https://www.homemadetools.net/forum/...453#post181839
https://www.homemadetools.net/forum/...8594#post87797
