As mentioned in the rescued from the dumpster thread, I found a 1973 Mercier placed in the scrap metal dumpster at Streel Level Cycles Workshop in Berkeley. Initially I thought it was tossed in the dumpster because it was missing one of the shift lever bosses. Later I spoke to a knowledgable friend who mentioned that bike was intended to be with only one Shift lever boss as the other Lever was clamp on. He further mentioned that the simplex clamp on for that bike went neatly around the boss to secure it in an attractive manner. I went back to the Workshop and dug through the bin of odd spare part down tube shift levers sure enough when i opened the bin the first Simplex Shift levers i put my hand on was the unique Simplex Clamp on Lever that I needed. No doubt it was stripped from my rescued Mercier. Bought it back for 5 dollars.

That was not uncommon to see on older bikes. It seems it would be pretty easy to put a second boss on the left side, but that would ruin the aesthetic of a bike that was intended for only a rear derailleur.

This was very common on French bikes sold in europe they offered five or four and ten speed editions of the same bikes. So the lesser bikes just did not have the second lever.Typically only the tens where imported to the US. Chances are they guy brought this low end sucker on trip and it brought in privetly through the college. Just a great bike for one found in this shape. Very interesting but not a lot of value.

There is so much to know about these old bikes; love that. Prior to my friend's input i was going to shave off the Boss and use clamp on shifters!

The UO-8 I sold last year (estimate it was a '73, give or take a year) had the same setup.

Please don't even consider shaving you can mount a clamp just above or below and make things work. Shaving great or even soso frames is stupid.

my uo-8 is also the same.

it makes sense, the bike came with rear deraileur and some of them had a front.

I don't agree with that. Only "so so" frames have that boss and a clamp-on above or below it is stupider.

That may be true of 70's frames, but not of earlier ones. I have seen many fine handbuilt frames from the 50's, including my 1954 Alvin Drysdale, that have the single Simplex boss just like that.

My late 60's Peugeot has the same set up. I like the flexibility that design brings as mentioned above by running 4, 5 or 10 speeds

I also had a '60s Follis that was All 531DB and had the same boss...I didn't think of it as "so-so", but...didn't keep it, either.

The best I've seen it on is a so so Peugeot PA10.

I'm not sure what the (French) thinking was but the single-boss was apparently fairly common place. I guess it seems to allow for either a single shift lever (just a 4 or 5 speed RD, no front) or the front was a "suicide lever" type and needed no cable. But Simplex has had a strap-type lever band designed just for this boss in catalog for a long time that added either the LH lever (as the OP's) or an earlier variation ('50s catalog) that paired both levers on the RH boss.

Those clamps are also handy when running a cable stop for an IGH setup. This Huret example I retapped for an M5 bolt and, yes, I did move it to above that stop on the frame:

Those single-lever clamps are also handy for mounting a rear fender to bike without a chain stay bridge bore:

slick kluges, you two!^^

I just got my hands on one of those double right-hand lever sets the other day. very cool, very rare - they show up on eBay occasionally in the $150 - $200 range.

Hopefully I'll have a project that makes use of it soon. it helps to have a frame that has the correct cable braze-ons as well, which is even rarer.