Praxis' conversion BB is designed to be a proper BB for Shimano Hollowtech cranks in either BB30 or PF30. Their patent pending design keeps the cartridge bearings outboard of the frame right on Shimano's spec for greater rigidity and free of frame/c-clip tolerance issues that other systems deal with. Simply press in the longer non-drive-cup, then the shorter drive cup threads into it. As the drive cup threads in, the trademark Collet system expands to a precise limit evenly dispersing pressure for a super tight fit. With both cups connected and the collet set exactly to spec, there is no chance the bearings can come out of alignment or wiggle/walk out of the frame. This design also uses a compressible o-ring on the non-drive side cup to compensate for frame shell width discrepancies.