The ZS44│EC44 headset is designed to fit frames with straight 44mm head tubes and can accomodate 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.