Shimano had an insert that looked like a derby or tophat that had to be used with some of their BB (IIRC the early octalinks) because the hole in the axle was larger than the sq taper hole and the extractor center bolt would not press on the axle. The tophat was dropped in and filled the gap. Sq taper axles will be about 5/8-3/4" diameter where octalink/Isis axles are 3-4mm larger in diameter. Not at home so can't be specific as to measurements.
Steve