Features and Benefits: Forged from the finest chrome-molybdenum alloy steel, the best choice for strength; Radius corner design extends the life of fasteners; design drives the side of the fastener instead of the corner; Design also avoids rounding of rusted or damaged fasteners; Black oxide finish and has etchings for identification; This is an impact socket and it is 20 mm. It is 3/'8 in. drive and 6 point. Designed to tackle the toughest jobs with solid durability and keeps them pounding job after job.