Just testing this still works. ;)
2 piece C-Mount to Pentax Q adaptor
1mm C-Mount shim (acts as a macro ring for focusing closer)
C-Mount Cosmicar/Pentax 8.5mm f1.5
40.5mm to 37mm step down ring
37mm variable ND deglazed
37mm to 52mm step up ring
I needed a shim between the Fujinon fisheye and my one piece C mount to Pentax Q adaptor.
Re-using the black rubber o-ring seal from the silver metal adaptor out of the Axis security camera was very handy. It is offering just the right flex to allow for smooth focus adjust that has enough resistance that stays put when I want it to. Acts like a makeshift helicoid I suppose. Give it a try if you did not throw out your o-ring already. Otherwise a similar size o-ring would do the trick.