Replacement Knob for Gwinstek GPD-3303S

[JenniferG]

For some reason I'm missing a knob to my GPD-3303S. It was sitting on the shelf for a while and it's just not there now lol.  I have no clue what happened to it and looked all over the place for it.

It's some sort of special D shaft or something.  I tried another D shaft knob and it wouldn't fit. 

Any ideas what knobs I can buy for this that would look decent. I can't seem to find replacement parts for it so probably will want to replace both knobs.

[xmris]

I think first of all is to measure the diameter of the shaft. As I can see on UK Farnell, there are various in the range of around 6mm.

[coromonadalix]

with the known hole diameter, you could find knobs with set screws ??

[Adrian_Arg.]

some friend, with a 3d printer:-//