781 A 1/4", Connection parts, 781 A/C x 1/2 x 36 mm x 1/4",Connection part 1/4", square head socket to 1/2", external square head. For manual and machine-operated tools (non-impact), with ball stop groove to safely lock the socket, knurling at the rear end for manageability during manual use, chrome-vanadium, dull chromed.