Abstract: The casing of an external leak tester for joints in oil well pipes is greatly reinforced in a compact manner by a cage which is symmetrical about two planes oriented at right angles to each other -- each plane containing the axis of the pipe to be tested. Four parallel pins interconnect the components of the cage, and one such pin (a lock pin) is retractable by piston means in order to permit the cage and thus the casing to open wide for lateral reception of the pipe. A plurality of means are provided to effect precise and rapid alignment of apertures in the cage, in order that the piston-operated lock pin may be inserted without binding to thereby lock the cage in closed condition. Cylinder-operated hooks are provided to effect augmented sealing compression of the sealing means for the test chamber, and to close the cage to the position at which the lock pin may be inserted as indicated above.