Best described by the Praxis Works website itself:
"Designed to be a proper BB for installing Shimano™ Hollowtech II cranks in either BB30, PF30, or Specialized’s OSBB frames. Our patent pending design keeps the cartridge bearings outboard of the frame right on Shimano™ 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, our trademark Collet system expands to a precise limit evenly dispersing pressure for a super tight fit. With both cups connected and our 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."