This will only fit variable resistor with the stem of 5.8-6mm thick

Spec:

• Knob height: 12mm
• Outer diameter: 17mm
• Outer shell wall thickness: 2mm
• Inner stem diameter: 6.15mm
• Inner stem wall thickness: 2mm
• Outer shell and inner stem height differences: 2.5mm
• Inner stem height: 7mm for the 2.5mm version, 8.5mm for the 1mm version
   

File version are the height spacing between top of the knob and the stem.

I printed it with transparent resin and lightly sand for the frosted look.