A pressed aluminium dome end for 101mm tube, giving fabricators a clean, ready-formed cap instead of rolling and welding a flat plate. The domed profile handles internal pressure far better than a flat end, which is why it is the standard approach for surge tanks, coolant expansion tanks and catch cans. Buy two and a length of 101mm tube and you have the basis of a tank in whatever capacity you need, with the welding face already machined so the joint sits square and needs minimal fettling. The 101mm size is the middle option in our range and suits medium-capacity surge and swirl pots where the 76mm dome would be too tight for the pump or pickup.