Acros az 55 zs55 3040 lower headsetbuilt for handling the intensity from mtb trails and road racing events, this versatile lower headset is essential for keeping your steering smooth and dependable. It features a durable aluminium construction, which allows it to withstand the increased pressure from longer road journeys as well as the aggressiveness of all day epics on your mountain bike. Coming complete with stainless steel bearings and an r3 seal, this lower headset gives you sleek operation in all weather conditions.features headset material aluminium bearing material stainless steelseal material r3 metal reinforced rubber use road, mtb steerer diameter 1.5 headset type semi integrated part number 4602601r1sbuy acros components from chain reaction cycles, the world's largest online bike store.