Rear derailleur mounting

[CC Rider]

I have Simplex downtube shifters and would like to use an old Simplex rear derailleur that's been lurking in a box.
Trouble is, the frame (with integral hanger) is threaed but the Simplex itself is threaded so mounts by 'pinching' onto the frame rather than screwing directly on.
The Simplex 'pinch' bolt has a short, plain shank that's a decent fit within the threaded frame (not sloppy but not tight) but is only about half the thickness of the frame hanger.
Is it a stupid thing to do and am I risking damaging the threads/frame by using clearly incompatible parts?
Thanks

 

[Jonny69]

Doesn’t sound right, but without a pic it’s hard to say.

 

[foz]

Some simplex mechs require a dedicated hanger. Not sure if they can be adapted for standard hangers