Abstract: A coupling is used for releasably connecting tools to the articulated arm of excavators and other heavy duty equipment. The coupling includes a first coupling member, a second coupling member, a locking member provided on the first coupling member and movable between lock and release positions, a spring arranged between the first coupling member and the locking member for urging the locking member into the lock position, and a hydraulically operated release mechanism provided on the first coupling member for moving the locking member into the release position in opposition to the force of the spring. Hydraulic fluid at a pressure relief pressure level is applied through a first non-return valve to release the locking member and permit detachment of one tool and attachment of another tool; the pressurized hydraulic fluid is then returned through a second non-return valve to return the locking member into the lock position, thereby retaining the newly attached tool under pressure of the spring.