11 includes a strap retainer 25 at the opposite end of the base 22 for retaining the other end of a strap or belt in a manner well known in the art the locking arm 23 of the plug member 11 includes a relatively thin planar portion 23a and a relatively thick hook portion 23b formed integral therewith and tapering as at 23c in the direction of insertion of the plug member 11 into the socket member 12 the hook portion 23b is recessed to provide a transversely elongated arcuate cavity 23d opening toward the base 22 and adapted to receive the complementary arcuate engaging surface 14b of the socket member 12 each of the retaining lugs 24 24 includes a stem portion 24a and an upwardly projecting abutment 24b normally spaced apart from the lower surface of the planar portion 23a of the locking arm 23 as shown in fig3 with this construction of the buckle 10 shown in fig1 4 the plug member 11 and the socket member 12 are coupled together by inserting the locking arm 23 through the entrance 19 into the guide channel 18 the locking arm 23 flexes downwardly about an axis in the planar portion 23a as the hook portion 23b engages slidingly with the inner surface of the upper shield 14 of the socket member 12 and advances to a point where the hook portion 23b snaps into locked engagement with.