Allstar 1/4 NPT and 9/16 Hex Head Engine Lifter Valley Vent (Pack of 8) fits small block Chevy applications. They are 1/4 national pipe thread and have a 9/16 hex head to ease installation. The lifter valley vents positively vent the crankcase and eliminate oil drain-through and windage loss. When used with valley screens, vents prevent damage from broken valvetrain components. They are sold as one set of 8 pieces and backed by a 90-day limited factory .