781 B 3/8", Connection parts, 781 B/A x 1/4 x 27 mm x 3/8",Connection part 3/8", square head socket to 1/4", 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.