referring now to the drawings and fig1 in particular , there is shown a strap fastener 10 which comprises a fastener body 11 , a mounting plate 12 and a socket member 13 all molded of synthetic resin . the fastener body 11 includes a base plate 14 having a laterally outwardly extending lug 15 at one or its upper end , a pair of co - axial pins 16 at the other or its lower end , a laterally outwardly extending locking prong 17 intermediate between the lug 15 and the pin 16 , and a laterally inwardly extending plug 18 opposite to the prong 17 . a flange 19 having a slit 20 extends upwardly from the lug 15 . the base plate 14 is provided adjacent to the lug 15 with a laterally elongated slot 21 so that the upper end portion of the base plate 14 posesses a certain degree of resiliency which is large enough to enable the lug 15 to tilt about its distal end upwardly away from the prong 17 . the fastener body 11 further includes a cover plate 22 having a plurality of laterally elongated openings 23 , 24 , 25 , 26 for the passage therethrough of a strap s , a pair of apertured lower flange portions 27 pivotally connected to the respective pins 16 of the base plate 14 , and an upper flange portion 28 having a locking projection 29 engageable in complimentarily shaped recess 30 formed in the lower surface of the lug 15 . the first opening 23 is defined between the flanged portions 27 and a first cross bar 31 ; the second opening 24 between the first cross bar 31 and a second cross bar 32 ; the third opening 25 between the second cross bar 32 and a third cross bar 33 ; and the fourth opening 26 between the third cross bar 33 and the upper flange portion 28 . the second cross bar 32 is slightly off - set from the common upper plane of the cover plate 22 so as to make the strap s lie substantially flush with the upper surface of the cover 22 . the third cross bar 33 has a longitudinal locking ridge 33a extending along its rear edge and projecting into the third opening 25 . with the strap s passed through any of the openings 23 - 26 , the cover plate 22 is rotated about the pins 16 in the direction of the arrow into coupling engagement with the base plate 14 as better shown in fig3 when the locking projection 29 is snapped into the recess 30 to hold the cover 22 and the plate 14 retentively together , while the locking prong 17 enters into the third opening 25 and holds the strap s immovably against the side wall of the third cross bar 33 . in this instance , the locking ridge 33a on the third cross bar 33 bites into the web of the strap s . the plug 18 , which extends laterally centrally from the base plate 14 in opposition to the locking prong 17 , has a hollow cylindrical configuration and includes a stem portion 18a integral with the base plate 14 and an enlarged head portion 18b separated by an interrupted annular shoulder 18c from the stem portion 18a . the hollow cylindrical plug 18 further includes a plurality ( four in the illustrated embodiment ) of longitudinal slits 18d in a criss - cross formation , as better shown in fig4 to render the plug 18 resilient and radially inwardly deformable . the head portion 18b has a tapered end 18e . the base plate 14 and the cover plate 22 may be conveniently , though not exclusively , fabricated by injection - molding in assembled condition . the mounting plate 12 to be interposed between the fastener body 11 and the socket member 13 is generally rectangular in shape and has a central aperture 12a for receiving a portion of the socket member 13 and a plurality of laterally extending anchoring posts 12b each with an axial blind hole 12c , there being four of these posts equally spaced around the central aperture 12a as better shown in fig8 . the socket member 13 , which constitutes another part of the strap fastener 10 , includes a substantially rectangular plate 13a and a cylindrical neck 34 extending centrally from the base plate 13a . the socket member 13 further has a stepped bore 35 extending through the base plate 13a and the neck 34 . the stepped bore 35 is composed of a small - diameter portion 35a extending concentrically through the cylindrical neck 34 , and a large - diameter portion 35b extending through the base plate 13a . the large - and small - diameter portions 35b , 35a are separated by an annular step 37 which is lockingly engageable with the interrupted annular shoulder 18c when the plug 18 is snapped in the stepped bore 35 . the inside diameter of the small - diameter portion 35a is substantially the same as , preferably slightly larger than , the outside diameter of the cylindrical stem 18a of the plug 18 . the outside diameter of the head 18b of the plug 18 is larger than the inside diameter of the small - diameter portion 35a and is smaller than the inside diameter of the larger - diameter portion 35b . as shown in fig6 the socket 13 is provided with a plurality ( four in number in this embodiment ) of countersunk holes 38 a locations registering with the anchoring posts 12b of the mounting plate 12 . with this construction , the mounting plate 12 and the socket member 13 are first brought into coupling engagement with each other by inserting the neck 34 of the socket 13 into the central aperture 12a of the mounting plate 12 through an opening in a substrate such as sheet of fabric or leather c of a knapsack , with the anchoring posts 12b received in the corresponding holes 38 . the lugs 12b may be plastically deformed by press or with heat to swell out and anchor within the countersunk holes 38 , thereby joining the mounting plate 12 and the socket member 13 with the fabric sheet c sandwiched therebetween , as better shown in fig1 . the fastener body 11 is then taken into coupling engagement with the socket member 13 , which has been united with the mounting plate 12 , by inserting the plug 18 into the stepped bore 35 . as the head 18b of the plug 18 advances along the small - diameter portion 35a of the stepped bore 35 , the head 18b is resiliently deformed radially inwardly . a further forward movement of the plug 18 causes the head 18b to be snapped into the large - diameter portion 35b due to the resiliency of the plug 18 . in this instance , the interrupted annular shoulder 18c is held in interlocking engagement with the step 37 t hold the fastener body 11 and the socket member 13 in coupled condition , as shown in fig1 . the back of the fastener body 11 is held in contact with the face of the mounting plate 12 . the fastener body 11 can be rotated at will in either direction about an axis of the plug 18 relative to the socket member 13 so as to adjust the lateral position of the strap s on the knapsack to suit the particular physical characteristics of the user . in this instance , the fastener body 11 undergoes smaller frictional resistance imposed by the mounting plate 12 than by the fabric c of the knapsack . the strap s can be also adjusted lengthwise by pulling its leading end in and out through the slot 21 in the base plate 14 of the fastener body 11 , for which purpose and for removal or attachment of the strap s there may be used for example a screwdriver d ( placed in the slit 20 in fig1 and then tilted in the direction of the arrow a ) with which to unlock or release the locking projection 29 from the recess 30 . fig1 through 14 show a modified form of strap fastener 40 which comprises a strap holder 41 pivotably connected at one end as at 42 to a base plate 43 and at the other end with a cross bar 44 around which is passed the strap s . the base plate 43 carries a plug 45 identical in construction and function with the plug 18 of fig1 a socket member 46 of the strap fastener 40 is substantially the same as the socket member 13 of fig1 with the exception that an elongate groove 47 extends arcuately in the face of a neck 48 to a limited angular extent about the axis of a stepped bore 49 . when the plug 45 is snapped in the stepped bore 49 , the groove 47 loosely receives a projection 50 on the back of the base plate 43 . with the groove 47 and the projection 50 thus provided , the fastener body 41 is rotatable only within the limited angular extent with respect to the socket member 46 and hence the fabric c of a bag . fig1 through 17 show another modified form of strap fastener 51 which comprises a fastener body or buckle 52 composed of a male part 53 and a female part 54 releasably engageable with each other . the male part 53 has at one end a cross bar 55 for mounting the strap s and at the other end a hook 56 releasably engageable with a abutment strip 57 formed on the female part 54 . the female part 54 includes a plug 58 extending from the back thereof and a projection 59 disposed adjacent to the plug 58 . the plug 58 is identical in construction and function with the plug 45 of fig1 . when the plug 58 is snapped with a socket member 60 , the projection 59 is received in an arcuately extending groove 61 in the face of a neck 62 of the of the socket member 60 . the angular movement of the fastener body 52 relative to the socket member 60 is limited to a certain extent by engagement of the projection 59 with ends of the arcuate groove 61 . many other modifications and changes may be made in the embodiments herein advanced , without departing from the scope of the appended claims . as for an example , the number of anchoring lugs 12b and openings 38 may be two or three as the case may be , or the lugs 12b may be substituted by rivets .
a strap fastener includes a fastener body on which a strap is retained , and a socket member adapted to be mounted on the fabric of a bag to retain the fastener body for connecting the strap to the bag . the fastener body has a plug with an enlarged head snappingly receivable in a stepped bore formed in the socket member . the fastener body is rotatable about the axis of the plug with respect to the socket member . with this construction , the strap is connected to the bag with utmost ease and can be adjusted in a desired posture to suit with the physical characteristics of the user .