I’m pretty sure Solo will have those.

 

Those one at Solo ? ; Shop Marshall AVT Silver Knobs - Pkg of 8 Online

 

I’m only trying to help OP, not looking for an argument here. Set screws are typically used on solid shaft pots. D or otherwise.

 

You must be able to align the mark (the black line) on the shaft in the correct position.
I would agree with you if there were no need to align a mark.

Here is a drawing that will help to better understand the problem, I hope.
If the set screw is on the round part of the shaft, it should be fine.

Who can tell where the set screw will be positioned before purchase of a knob ?

 

We haven't heard back from Bob Hosaluk about our suggestions after all, it's his amplifier that's involved.

 

 

Right , answer #5