781 C 1/2", Connection parts, 781 C/B x 3/8 x 35.5 mm x 1/2",Connection part 1/2", square head socket to 3/8", 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.