as may be seen from a consideration of the drawings , and with particular reference to fig1 the c - ring of the present invention comprises a main body 10 in a generally circular configuration . a radial slit 11 is provided between the ends 12 and 13 of the body 10 and , the ends 12 and 13 are provided with inwardly directed projections 14 and 15 respectively . for reasons more fully explained below , the thickness of the ends 12 and 13 is substantially greater than the thickness of the back 16 of the ring . in use , the ring 10 is employed for fastening a plurality of sheets 20 in a looseleaf , freely pivotal , relationship . as can be seen clearly from fig2 the sheets 20 are provided with one or more apertures 21 having a length greater than the axial length of the individual c - rings 10 . the sheets 20 may be placed upon the ring by manually separating the ends 12 , 13 by springing them apart and inserting the sheets . release of the sprung ends 12 , 13 will automatically permit the closure of the ring . although the drawings illustrate the ends 12 , 13 somewhat separated , in actual practice , it is preferred that they be touching and in typical examples , i have found that the ends 12 , 13 do in fact touch in most instances . however , as is generally known , a typical sheet of writing paper approximates 0 . 003 of an inch in thickness , while many bound materials are substantially thicker . accordingly , slight separation of the ends 12 , 13 will not , in normal operation , create a problem until the separation exceeds the thickness of the materials being bound . moreover , even in the event of slightly larger separation , however , the specific structural design of the c - ring of the present invention substantially prevents inadvertent separation of the sheets from the c - ring binding . as can be seen from a consideration of fig3 sheets 20 , may readily be pivoted , such as illustrated by sheet 20a in fig3 . sheet 20a has been pivoted counterclockwise , in the direction of the arrows 20b and 20 c from a position overlying the sheets 20 on the right hand of fig3 . as the sheet 20a has been pivoted in a counterclockwise fashion , the edge 21a of opening 21 thereof has contacted the inwardly hooked projection 14 of the end 12 and has caused the ring to rotate in the direction of the arrow 20c , along with the sheet 20a . it has been found that this rotation of the ring with the sheet is the typical mode of operation , entirely absent any conscious design by the user of the binding . in practice , this prevents the sheet 20a which is being manipulated , from being in a position to leave the binding via the slot 11 and , further , as additional sheets 20 are flipped in the counterclockwise direction , following movement of the sheet 20a , the slit 11 has been moved and is no longer in a position to permit egress of any of the sheets from the binding element . thus , the internal projections 14 and 15 provide a mechanical interlock , in effect preventing any inadvertent disassembly of the sheets from the binding elements . it has been found in general practice that where a plurality of c - rings are employed in a binding , the possibility of all of the slits 11 being aligned to permit removal of a bound sheet , is remote , and for all practical purposes , non - existent . in a typical ring found satisfactory for binding purposes in accordance with the present invention , the axial length of the ring was 1 / 4 inch , the internal diameter of the ring , shown at 23 in fig1 comprised 3 / 8 inch and the external diameter comprised approximately 1 / 2 inch . the ring , used with aligned paper openings of a width of 3 / 16 inch , may satisfactorily have ends with a thickness t of approximately 5 / 32 inch which helps insure hooking contact of the edge 21a by the projection . in the manufacture of such a ring , an initial mold spacing between the ends 14 , 15 of approximately 15 / 1000 &# 39 ; s of an inch , substantially exaggerated in fig5 will provide a complete subsequent closure of the ring upon ejection from mold 25 , where thermoplastic materials such as nylon or delrin are employed . a consideration of the mold shown in fig4 illustrates that the cavity takes substantially exactly the form of the c - ring in repose , except for the built - in end separation . the ring is ejected from below , as viewed in fig4 by a plurality of typical mold ejection pins 26 . for example , an ejection pin may be provided to move axially of the c - ring and shut against the ends 14 and 15 as well as the back 16 . to provide a sufficient plastic material to support an ejection pin at the back 16 of a bulbous protrusion 16a is provided . a very slight mold draft , or relief , of one or two thousandths of an inch is provided to permit ejection of the molded ring , and plastic material may be inserted into the mold cavity as illustrated in fig5 by any conventional means , such as for example , by way of a hole 28 through the mold plate 27 lying flat over the top of the cavity as shown . i have found that molding the c - ring provides clean , sharp , corners without burrs and post - mold shrinkage provides a closed slit and , accordingly , it is preferred that the c - ring be individually molded rather than cut from a length of continuously extruded material . it is noted , however , that transversely cut extrusions , having a cross - section as shown in fig1 can be employed where a less finished product is acceptable , such as where stiff sheets 20 are used . as mentioned above , it is desired that the ends 14 , 15 be heavier than the back 16 of the ring . this causes the rings to hang downwardly when carried on a rod or mandrel , such as shown at 30 in fig1 having a diameter less than the diameter 23 . in automated binding equipment , the protrusion 16a also aids in achieving and maintaining such an alignment by cooperating with a grooved surface on the supporting mandrel 30 . such binding equipment is the subject of the copending application of henry n . staats and frederick h . melull , filed of even date herewith . various materials , which will shrink during cooling after being molded , are acceptable for the construction of the c - ring of this invention . i have found high molecular weight polyamides ( such as nylon , marketed by e . i . dupont denemours & amp ; co . ), a rigid polyvinyl chloride and delrin ( an acetal resin manufactured by e . i . dupont denemours & amp ; co ., inc . ), satisfactory materials . they are resilient and yet stiff enough to return to their original shape following insertion of sheets . although the named materials are thermoplastic materials , thermosetting materials may also be employed . the internally projecting ends 14 , 15 may take various shapes . the curved hook shape illustrated in the drawings , fig1 and 5 , provides optimum performance , however . it has been found that with the surfaces becoming substantially radial adjacent the slit , sheets are hooked and operate to pull , or rotate , the ring rather than ride over the projection . accordingly , a rather abrupt projection is preferred . since variations may readily be provided without departing from the scope of my invention , it is intended that the scope of the claims be limited solely by that of the hereinafter appended claims .