The ZS44/EC44 headset is designed to fit frames with straight 44mm head tubes and can accommodate straight and tapered fork steerers with the appropriate crown race. The "ZS" stands for "Zero Stack" as the section of the cup that houses the top bearing sits inside of the frame's head tube while "EC" stands for "External Cup" meaning the section of the cup that houses the lower bearing sits outside of the frame's head tube. The "44" stands for the diameter of the "skirt" that presses into the frame. Made in the USA. FEATURES - U.S. sourced 6061-T6 aluminum - Machine engraved White Industries logos - Easily replaceable Enduro bearings - "Split" crown race for tool-free installation and removal - Really sweet matching headset spacers available separately SHIS specification - Upper: ZS44/28.6 - Lower: EC44/40 HEAD TUBE: - Top 44mm - Bottom 44mm STACK HEIGHT: - Top 8mm - Bottom 12mm STEERER SIZE: - Top 1 1/8" (28.6mm) - Bottom 1 1/2" (40mm) WEIGHT: - 106 grams