"Press Fit" and "Drop In" headset bearings are located inside the steerer tube which results in a lower stack height. In contrast to "Press Fit" headsets "Drop In" headsets don't have to be pressed in. The bearing rests directly on the angled (36° or 45°) surface of the steerer tube.
Full complement angular contact cartridge bearings packed with Ritchey high-webbing grease
Stack Height: 12.9mm
Lower Fit (S.H.I.S.): ZS55/40
Upper HT OD/ID: 50/40
Lower HT OD/ID: 61/55
Bearing: Sealed Cartridge (ACB)
Buy Ritchey Logic Zero Pro Press Fit Headset from Chain Reaction Cycles, the worlds largest online bicycle store.