Fine NPT (nominal pipe thread) size. Our plastic bung plugs feature a 3/4" knock-out plug designed into the barrel plug for adapting faucets, pumps etc. Great replacement threaded plug to fit most 55 gallon water barrel and drum sizes.
White 2" Poly Bung Cap Fine Thread. Will fit all UN standard 55, 30, 15 gallon barrels.
Please note that most 55 and 30 Gallon UN Poly Barrels sold in the US have one (1) course thread and one(1) fine thread 2" cap. These are the fine thread cap, with a 3/4" tap in center for pumps and accessory attachments.