resilient retention prongs 14 b are disposed on the inside of receptacle 12 just beneath its top surface and the protrusions 14 c are disposed in outwardly facing relation to be received in the holes 8 in the top surface of the metal case 7 of the plug 5 from the underside thereof in this modification retaining member 16 has a generally rectangular outwardly extending tongue portion 16 c which is disposed in a position to be slidably received inside of the receptacle 12 and on the underside of the retention prongs 14 b when the longer leg 15 a of the shackle 15 is moved inwardly relative to the housing 11 the retaining member 16 moves axially outward such that its tongue portion 16 c is moved to a locking position covering a sufficient portion of the retention prongs 14 b to retain the protrusions in the engaged position in the holes 8 of the plug 5 all of the other components are the same as described previously and are assigned the same numerals of reference and operate as described previously but will not be described again in detail to avoid repetition in the embodiments equipped with a shackle a security cable may optionally be secured to the shackle of the lock whereby the memory device secured to the lock can also be secured to another.