2″ Vented Bung – Steel Drum The Tri Sure 2″ Vented Bungs are designed to fit in the 2” BSP opening on Tighthead Steel Drums. They can also fit on Open Top drums, assuming they have the 2” opening fitted in the lid. They work by allowing air to flow out of the drum, reducing the build up of pressure. Produced from zinc coated, mild steel and have a black washer/gasket.