A theft deterrent device for "bolting" pieces of material together, comprising:
(1) a nut-like device having a smooth outer surface resistant to the effects of conventional wrenches,
(2) a male threaded member having an internally threaded axial bore, adapted to threadedly engage the nut-like member,
(3) a locking screw for threadedly engaging the internal bore of the male member, and having a head that mates with the smooth outer surface of the nut-like device, resulting in an essentially smooth, continuous outer surface resistant to removal using conventional wrenches, and
(4) an environmental plug for inserting into the driving recess or bore of the screw to prevent foreign and corrosive matter from entering the recess. The locking screw threads are of opposite hand to that of the nut-like portion, so that the locking screw must first be removed before the nut may be removed. With the locking screw in place, the driving recess of the nut is inaccessible, the locking screw head having conformed to the configuration of the nut to form an essentially uniform, smooth and continuous outer surface which is virtually resistant to the effects of conventional wrenches.