Semi-integrated headset (zs) with steering stop for frames with 66mm head tube at the bottom. The Acros blocklock-zs66-headset-lower-part protects your top tube and down tube from contact with handlebars, attachments and the fork crown as well as the wires and cables from overstress in case of a crash. Compatible with all forks with a 1.8″ steerer tube (46mm) at the crown.Key Features Inner diameter (ID): 66mm Outer diameter (OD): 72mm Fork steerer (SD): 46mm / 1 1/8″ Available turning angle: 120 Height (H): 2.8mm Total stack height(D): 16.5mm Weight: 95g