Hot socket gap indicator.
https://diqn32j8nouaz.cloudfront.net...r_fullsize.jpg
How it works (2:21 video):
https://www.youtube.com/watch?v=j-r3IdZW0UE
Previously:
https://www.homemadetools.net/forum/...007#post230045
https://www.homemadetools.net/forum/...500#post135831
https://www.homemadetools.net/forum/...887#post229708
https://www.homemadetools.net/forum/...171#post218174
https://www.homemadetools.net/forum/...911#post217263
