Telecaster knob for a 2mmx5mm switch blade; usually used on American Telecasters and replacement switches.
The tolerances are purposely a bit tight so that you need to gently force it on so that you don't loose it, like you do most other switches.
To have a smooth finish print in ABS and give the part an acetone vapor treatement.
This self designed and printed knob sits on my self designed and build Telecaster. How cool is that, that these days we can pretty much produce it all at home.