A barrel lock for locking various utilities devices such as valves, meters, or enclosures associated with the control or distribution of gas, water or electricity includes a shank with a single driven ball that can be forced radially outward from the shank to lock onto a cap-like retainer such that the utilities device is restrained between the retainer and an enlarged head of the shank. Preferably, only a single driven ball is used to concentrate the clamping force at a single point, thereby creating an exceptionally high clamping pressure. For even greater clamping force, an accurately and strategically positioned end stop allows a drive ball to push against the driven ball at an extremely shallow angle of attack while preventing the two balls from accidentally toggling over center and irreversibly locking up. The barrel lock has infinite variable adjustment in an axial direction to fit a wide variety of devices.