[Latole]

View attachment 617940​

Right , answer #5

 

[Latole]

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

 

[Latole]

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 ?

 

[Latole]

The set screw makes me think it would work.

Nothing is certain, far from it. Even very little chance.
Have you ever tried it on a “D” shaft? I have.

 

[Latole]

These. $2.69 each

View attachment 617820

These are for round shaft not "D'" shaft.
If OP can make shaft round, it will fit.

Marshall AVT knobs ;

 

[Latole]

I’m pretty sure Solo will have those.

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