Acros ai 52 is52 3040 lower headsetperfect for updating your existing lower headset interface, this lower headset features a resilient aluminium construction. This makes it capable of handling the increased pressure on all day epics on your mountain bike as well as long distance rides on your road bike. Allowing your fork's steerer to rotate inside your frame's headtube, this lower headset is equipped with stainless steel bearings. This gives it an extra layer of durability in both wet and dry riding conditionsfeatures headset material aluminium bearing material stainless steel seal material r3 metal reinforced rubber use road, mtbsteerer diameter 1.5headset type integratedpart number 4802601r1sbuy acros components from chain reaction cycles, the world's largest online bike store.