2″&3/4″ Metal Flanges ,Zinc Plated With Passivation In Cr3 and Cr6 or as per customer request . Steel drums/barrels  typically have two openings (bung holes) with flanges, 2″ and 3/4″ in diameter, in the top of the drum/barrel (or cover for open head drums). The flanges are the closure fitting s that are permanently inserted into the drum and provide the receiving threads for a plug. Most steel drums have NPT (National Pipe Thread Taper) threaded openings. Unlike straight pipe threading, NPT threaded fittings will pull tight to make a liquid-tight seal.Once drums are filled with liquid,  drum plugs ( drum bungs) are screwed in the flanges using pneumatic or hand operated bung tightener (plug or torque wrench). To secure the contents of the drums against theft and adulteration during shipment, drum cap seals are used. These drum cap seals sit on top of the flanges and are sealed  using drum cap-seal crimping tools (also called drum cap sealers). Once drum cap seals are crimped, the plugs can be unopened unless  by destroying the drum cap seals.