So I recently installed Dia Compe inverse brake levers (22.2mm) on my VO Montmartre handlebars (also 22.2mm). Now that I've routed the cables and hooked up the brakes, if I pull the brake lever, the entire thing starts pulling away from the end of the handlebar and the lever goes slack. I think it is because the mechanism does not fit inside the handlebar snugly enough.

My question is: why is it doing this even though the sizing is correct, and is there any way to make the fit tighter? I've wound the nut down on the bolt as far as I can using my own strength and am about at my wit's end!

Lefty/tighty, correct?

The Montmarte bars come in both 22.2 and 23.8. Are you sure they sent you the right ones?

If they are the bars from velo o-they are road bike size (23.8) If not marred up-return the levers for the right size; or shim them [pita tho]

I don't think so.

I'm afraid I'm quite sure I purchased both the bars and the levers in 22.2 (even checked my receipts). Perhaps VO sent the wrong size, but I don't know how I'd know for sure! Really frustrating.

This is why you need a caliper. If you don't have one, you can employ your HS geometry: wrap a strip of paper tightly around the bar, mark (with a sharp knife) where it overlaps, unroll, measure the length very carefully, and divide by pi (3.14). Don't try it without removing the bar tape.

If you don't like math, just mark the paper as above, then wrap it around your stem quill. That should be the same 22.2 diameter.

I've not used the Dia Compe inverse levers. I thought they were like Bar Cons. The Tektro inverse levers I had were that way, I believe.

Just revisited the VO site-googled Montmontre-says they are road size. Smaller operation than you would think. A lot of younger peeps working in the order dept. Mistakes happen-I'm sure they will work with you.

I'm not sure what you're looking at. When I go to the product page it clearly states that the bars are available in both road and mtb sizes, and goes on to specify what will fit on or in each type.
https://store.velo-orange.com/index.p...handlebar.html