Originally Posted by
hank0604
Not sure if this is what you're talking about, but: when I switched from a flat bar to bullhorns I had a brake compatibility issue. The old handlebars were 31.8 and the new ones 26.0, so the brakes (cross style levers) wouldn't clamp tight enough. The shop had some shims that solved the problem.
Reverse brake levers go into the open ends of the bullhorns like so:
Usually to fit snug in the hole, the inserting end has an expanding wedge when tightened. genjy's problem seems to be that the hole of his bars is already too small.