3pc UNIVERSAL JOINT set - wrench - socket sizes = 1/4" - 3/8" - 1/2" IMPACT GRADE Universal Joint Sizes: 1/4", 3/8", and 1/2" Dr. Drop Forged, Heat Treated Steel. Oil-Quenched, Black-Oxide Finish for Durability Holes on Two Largest Universal Joints for Locking onto Drive Tang Spring-Loaded Ball Bearings Hold Sockets Securely Ball/Swivel Action Universal Joints Gives Sockets Access in Tight Areas