A plurality of circumferentially-spaced driving lugs are formed on the improved square-drive tang of a wrench, such as a ratchet wrench; and these driving lugs cooperate with a corresponding plurality of recesses or pockets formed in the top portion of an improved interchangeable square-drive socket,...http://www.google.es/patents/US5910197?utm_source=gb-gplus-sharePatente US5910197 - Wrench with supplementary driving lugs formed on its square cross-sectioned drive tang and interchangeable sockets therefor
Wrench with supplementary driving lugs formed on its square cross-sectioned ...
