Acros ai 42 is42 28.6 upper headsetproviding a smooth rotatable interface between your bike's fork and headtube, this upper headset gives you dependable steering performance. It features a rock solid aluminium construction, which makes it more than capable of handling all the abuse that's associated with road racing and mountain bike trail riding. Coming equipped with stainless steel bearings and an r3 seal, this is a perfect upgrade for reliable performance in all weather conditions.features headset material aluminium bearing material stainless steel seal material r3 metal reinforced rubber use road, mtb steerer diameter 1 1 8 bearing fit 42mm total stack height 13mm headset type integrated part number 2602605r1lsweight 50g approxbuy acros components from chain reaction cycles, the world's largest online bike store.