The 40-Series is the workhorse of Cane Creek&';s headset line-up and incorporates all the features necessary for a durable, lightweight and long-lasting headset while offering the perfect balance of performance, durability and value Contoured and relieved 6061-T6 aluminum for minimized weight and maximized strength with split-lip sealed stainless steel bearings Low friction, dual-seal crown race and top cover provides maximum sealing from contaminants, plus a captured compression ring design for carbon steerer compatibility (Interlok spacer compatible, sold separately) Cane Creek Integrated 41.0mm ID (36x45), Campy Hiddenset 42.0mm ID (45x45) , ZS (ZeroStack), or EC (traditional, External Cup) available for 1", 1-1/8" and tapered steerers Carbon indicates a carbon top cover on upper cup Internal parts are cross-compatible across the 10, 40 and 110 series Please see: www.canecreek.com/headset-fit-finder for fit information ZS44/56 includes headset cups and crown race