This Teng Tools socket is a professional, bi-hexagon 1/2in Square Drive socket. Size: 9mm. The TENM120509 Bi-Hexagon, 12-point socket has the following specifications AB 36-38 & 55-56, BT (all), FK 17-21, HS (all), IM (all), IV (all), KA 27-28, KW (all), PA 20-99, PH 15-99, ZE (all), Channel Islands.