These are 1/8" NPT threaded aluminum bungs. They are 6061 aluminum. 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 Packs of 4