I bought a 2nd hand Line 6 POD HD Pro which was missing two of the knobs for the encoders under the screen.

The knob is slightly differrent from the original in that it has sharper edges and is not glossy. It is also slightly shorter than the original to deal with the lack of 2mm hollow at the base of the pot.

When its installed, unless you are close enough to use it, you can't tell its different.

It should be a snug push fit onto the D shaped shaft of the pot. You may want to use a scalpal to slightly bevel the hole for the shaft to remove any elephant foot that might make the opening of the whole too small.

This file was created using the openscad file uploaded by Steve Cooley (thanks Steve).