Jeez, I don't think this is really complicated, unless you've never taken a set of bars out of the stem before. The clamp diameter (25.4, 26.0 etc) refers to where the stem clamps. This is pretty much always bigger than the diameter of the rest of the bars. It has to be, because if it wasn't, how would you get the stem round the curves and into position? (it's hard enough anyway) Most bars have a small bulge which is completely covered by the stem clamp, but some bars have a wider bulge, or instead of a bulge, ramp up from the normal bar diameter to the clamp diameter in a smooth slope. Cinelli bars, for instance, have a wide area either side of the stem thats larger than the rest of the bars, which is always engraved with logos etc. The Paul lever won't sit on this bit, and neither will any other lever designed for normal bars. Lecture over.