The RP Series plugs provide a general purpose, high-strength, machine thread plug adaptable to a multitude of applications. Originally designed for automotive and air conditioning tube fittings. Serrated for finger tightening, they also have a slotted hex-head for screwdriver, nut driver or wrench installation where desired. : : A:.69, B:.44, C: 1.03, D:.28, TOFITTHRSZ: 3/4-16.