A BB30 bottom bracket does fit in a 68 mm wide shell, but not the common BSA, 68 mm wide, threaded shell. That takes a threaded cup bottom bracket of one type or another. The BB30 bottom bracket is just a pair of cartridge bearings with snap ring retention clips that sit behind them in the shell. The BB30 shell is not threaded as the bearing cartridges are pressed into the shell for a tight fit.