The knurled knob is an inexpensive stainless item I bought online (Amazon) for another project and didn't use. You will want one with 3/16 or 1/4" female threads, or metric equivalent. I then made a small channel cut the width of the key across the drilled face, then cut off and shaped the end of the key to insert into the hole as well as index into the channel. Epoxy holds it together, with the turning force taken by the key in the cut channel, so it's very solid.
To get it to match the finish of the existing switches, I glass bead blasted the knob portion, then oiled it with ACF-50.
That is really nice, just leave the key in place and few people would know how to work it.
You wouldn’t still have a link to that knob would you?
