US Patent [1989-01-10] - Clutch type socket wrench (US4,796,492 Liou, Mou-Tang)
A socket wrench comprises a handled hollow head receiving a torque transmitting sleeve member which is provided with peripheral teeth to engage with inwardly extending teeth of the hollow head. The teeth of both the hollow head and the sleeve member are elongated axially and formed in such a manner that their height from their intermediate portion gradually reduces towards the two ends thereof and their intermediate portion is notched to receive a C-shaped locking ring that interengages the hollow head and the sleeve member. The teeth can engage with each other when the handle is turned upward or downward to cause the axis of the hollow head to incline the axis of the sleeve, and to disengage from each other when the axis of the hollow head is in alignment with that of the sleeve. Link to USPTO.