These are 1/8″ NPT threaded steel bungs. They are 1018 cold rolled steel. 5/8″ in diameter, and 5/8″ in length, with the flange being 7/8″ outside diameter and 1/8″ thick. Drill a 5/8″ hole and drop your bung in and the flange holds it perfectly straight and in line. Great for oil and gas tank fittings. Sold in 4 packs. Made in Ohio, USA National Pipe Thread (NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings. The taper on NPT threads allows them to form a seal when tightened. These are NOT used for mounting bungs as standard bolts do not fit into the tapered NPT threads.