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

 

[daccordimark]

My wife's old Gitane had that type of Simplex rear mech and the frame had the special hanger to match. Made it impossible to upgrade the mech.
I never tried putting the Simplex on a standard hanger but it seems a bad idea to me. They're not designed for each other and if you mess up the hanger the frame then needs an expensive repair.

https://www.disraeligears.co.uk/site/simplex_derailleurs_-_1971_page_3.html - shows the offending part.

 

[SteelNipple]

Here, Campagnolo 1010/B dropouts with Gipiemme branded Simplex LJ4000



The Portacatena bulge sets the bolt somewhat not flush and at an angle

 

[bulgie]

I have never seen a Simplex mech newer than maybe mid-'50s that wouldn't bolt right on to a Campy or similar threaded dropout. You don't use the threads, but they don't hurt you one bit.

Some ancient mechs used a hanger that was bent out wider than the hub axle attachment part, like this:


But those mechs are the plunger-type, no parallelogram. I doubt you're trying to mount one of those! Any Simplex with a parallelogram will bolt right on.

You can't go the other way though, no putting a Campy mech on an old Simplex hanger, without modifying the hanger first. The mods don't hurt the hanger any though, it'll still work fine if you go back to a Simplex later. Here's the mod, tapping threads and filing a rotation-stop:



The hole is already the right size for tapping to M10, just make sure to run the tap in very "normal" (perpendicular).