Knurling tool. By Made in Poland. 5:46 video:
https://www.youtube.com/watch?v=Mukakb6Dq9U
Previously:
https://www.homemadetools.net/forum/...383#post177378
https://www.homemadetools.net/forum/...012#post176063
https://www.homemadetools.net/forum/...666#post163119
https://www.homemadetools.net/forum/...451#post162177
https://www.homemadetools.net/forum/...920#post160214
https://www.homemadetools.net/forum/...990#post156974
https://www.homemadetools.net/forum/...879#post152609
https://www.homemadetools.net/forum/...134#post149632
https://www.homemadetools.net/forum/...657#post147667
https://www.homemadetools.net/forum/...902#post119677
https://www.homemadetools.net/forum/...758#post143897