Acros ai 42 is42 30 lower headsetdesigned for handling the intensity from road racing and all day epics on the mtb trails, this lower headset gives you a smooth rotatable interface. It features a hard wearing aluminium construction, which means you'll benefit from its incredible strength without adding any unnecessary weight to your bike. Coming complete with stainless steel bearings and an r3 seal, this lower headset is an ideal upgrade for reliable steering performance in all weather conditions.features headset material aluminium bearing material stainless steel seal material r3 metal reinforced rubber use road, mtbsteerer diameter 1 1 8headset type integratedpart number 3902601sbearing fit 42mmtotal stack height 13mmweight 50g approxbuy acros components from chain reaction cycles, the world's largest online bike store.