These kits come with an aluminum female bung that can be welded to aluminum, tanks, valve covers, filler neck plates and other locations to replenish fluid or serve as an insection port. Three kits are available, Knurled Filler Cap with 1.5" O.D. Female weld bung contoured grip for easy removal and installation with either Moroso or Competition Engineering logo, 2.6" O.D. weld bung. Filler Caps are machined from 6061-T6 aluminum and include an O-ring for leak free sealing.