Acros ai 41 is41 28.6 upper headsetdesigned for reliable steering performance, this upper headset features a tough aluminium construction. This makes it perfect at handling the intensity from clocking up the miles on your road bike, as well as the aggressiveness from technical mountain bike trails. Kitted out with stainless steel bearings, this upper headset allows your fork's steerer to rotate smoothly inside your frames headtube. This means you'll benefit from its extra durability as well as its sleek operation.features headset material aluminium bearing material stainless steel seal material r3 metal reinforced rubber use road, mtbheadset type conventionalmanufacturer part number 2402605r2lsbuy acros components from chain reaction cycles, the world's largest online bike store.