The Radium Coolant Expansion Swirl Tank features three ports that use -6AN to 9/16-18 O-ring adapters (not tapered pipe threads) for a positive seal. The main tank is a 2-piece design constructed of cast aluminum. The two halves (shown below) are welded together along with a CNC billet aluminum cap receiver which mates to any standard 32mm "import" style pressure cap. Coolant expansion tanks are necessary for proper air bleeding in applications that utilize a low mounted radiator. The Radium Engineering tank also has an internal swirl feature. Hot pressurized coolant from the cylinder head is sent into the vortex chamber's inlet tangentially and accelerated to a high rate of rotation. This is an old hot rod trick to help aid in deaerating the system.