US Patent 7159493 Driving bit linking device in a box wrench

A driving bit linking device in a box wrench includes a box wrench on a handle having a central bore, a pair of checking slots of different level in the opposing middle peripheries, an annular collar on a lower periphery and an annular groove in an upper periphery for disposing a retaining ring, a bottom spring disposed in the circular section of the central bore, a pair of compression springs wrapped on the outer periphery each including a transverse checking rod respectively inserted into the hexagonal section of the central bore through the checking slots and a cap wrapped on the box wrench and secured by the retaining ring. It is characterized that this device is capable of linking up a C type bit, a E type bit and even a double tips bit.