Abstract: A shrouded jam locknut including a body member of frustoconical configuration having a larger base and a smaller base, a recess extending inwardly into the body member from the larger base and terminating at a shoulder for bearing against a nut in locking relationship therewith, a threaded bore extending inwardly into the body member from the shoulder for receiving the end of a threaded shank, a skirt surrounding the recess and terminating at an annular edge, and a key-receiving recess in the smaller base.

Abstract: A pipe plug which cannot be removed from a pipe with the same key with which it is installed, the pipe plug having a body with a plurality of arcuate grooves having inclined arcuate ramps leading from its face into its body and terminating at shoulders for abutting engagement with first key having pins which bear against the shoulders to tighten the plug in the pipe but which cannot loosen the plug because the pins will ride up the ramps and cam out of engagement withthe plug, and a second key for removing the plug including a ridge on the second key for mating with a complementary curvilinear groove in the plug. A counterbore is provided in the face of the plug to receive portions of the ridge which are of substantially the same diameter as the counterbore to thereby center the second key with respect to the plug and guide it while the second key is rotated until the ridge thereon falls into the groove to effect mating engagement therewith.

Abstract: A tamperproof construction for preventing actuation of the actuating nut of a fire hydrant comprising a nut actuating body for receiving the hydrant nut in turning relationship, set screws locking the nut actuating body to the actuating nut, a shroud permanently secured on the nut actuating body by means of a snap ring so that it covers the set screws but is rotatable on the nut actuating body, a bore in the shroud for permitting selective access to the set screws, a key-operated plug in the bore, a cap permanently and rotatably mounted on an end of the nut actuating body which protrudes through an opening in the shroud, and a limited axial portion of the nut actuating body exposed between the cap and shroud for receiving a specialized wrench.

Abstract: A manhole cover locking bolt construction for locking a manhole cover to an associated frame including a bolt having a threaded shank and an externally threaded head and an endless curvilinear groove in the top of the head for receiving a key of mating configuration for threading the bolt into and out of the manhole cover frame, and a cap for threadably mounting on the externally threaded head to protect the curvilinear groove against entry of foreign matter.

Abstract: A pipe plug which cannot be removed from a pipe with the same key with which it is installed, the pipe plug having a body with a plurality of arcuate grooves having inclined arcuate ramps leading from its face into its body and terminating at shoulders for abutting engagement with first key having pins which bear against the shoulders to tighten the plug in the pipe but which cannot loosen the plug because the pins will ride up the ramps and cam out of engagement with the plug, and a second key for removing the plug including a ridge on the second key for mating with a complementary curvilinear groove in the plug. A counterbore is provided in the face of the plug to receive portions of the ridge which are of substantially the same diameter as the counterbore to thereby center the second key with respect to the plug and guide it while the second key is rotated until the ridge thereon falls into the groove to effect mating engagement therewith.

Abstract: A tamper-proof bolt including a shank with a threaded end portion merging into an unthreaded portion of lesser diameter merging into an enlarged unthreaded portion merging into the larger base of a frustoconical head also having a smaller base, an undulating curvilinear groove in the smaller base, an island having lobes within the groove, an outer side in the groove, an inner side in the groove formed by the sides of the lobes of the island, and a cylindrical boss on the island extending axially outwardly from the smaller base and having a radial dimension which is approximately equal to the minimum radial dimension of the undulating groove.