Rear derailleur mounting

Good thread ......

Personally in the OPs case, if it was me, I wouldn't even bother with the Simplex RD although in all chance it would probably work. Simplex really went about things in a strange way and I would almost argue best pass the Simplex RD along to someone who may need it for a frame with a Simplex dropout.

Pretty sure the Simplex downtube shifters would work with practically any rear mech.

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The OPs fixing is the variety in the green box and like mentioned the stop tab position is towards the top (should work with any dropout). The other variety is in the red box with a totally different upper pivot, used with a (thin) steel hanger plate and the stop position is interfaced directly between hanger and the rear mech with no stop tab.

Often thought - especially in the case of wanting to fit a Campag / Shimano rear mech to a Simplex dropout - is to have a specific upper pivot machined and stop plate on very similar lines to what the fitting is in the red box. I personally think any frame modification requires a bit of careful consideration prior.
 
Hi,

I’d be cautious. The frame’s threaded hanger is really meant for a derailleur that screws in. Using a Simplex pinch-type with a thin bolt could damage the threads over time.
If you really want to use it, look for a vintage Simplex adapter that fits threaded hangers safely. Otherwise, stick to a derailleur meant for threaded mounts.
 
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