Single-fin fastener
BACKGROUND OF THE INVENTION 
     The present invention relates to a single-fin fastener for attaching a base member to the hole of another member such as a panel. 
     FIG. 1 shows a conventional single-file fastener B comprising a support board 1 integrally formed on a synthetic resin base member A and projecting therefrom, and an engaging fin 3 having a flexible hinging butt 2 at the tip of the support board 1 and extending from the tip of the board 1 in a direction opposite to that of the projection of the board. The engaging fin 3 includes an engaging notched portion 3a near the movable tip of the fin. FIG. 2a shows the state that the synthetic resin base member A is attached to the hole 4 of a panel C by the single-fin fastener B. When a force F of 4 to 5 kg acts on the base member A in such a direction as to pull the member out of the hole 4 of the panel C, as shown in FIG. 2B, stress concentrates on the structurally weakest flexible hinging butt 2 so that the engaging fin 3 is opened to a limit. As a result, the single-fin fastener B is easily pulled out of the hole 4 of the panel C, starting with the support board 1 of the fastener. This is a problem. 
     SUMMARY OF THE INVENTION 
     The present invention was made in order to solve the above-mentioned problem. 
     Accordingly, it is an object of the present invention to provide a single-fin fastener which has an advantage of being a compact attaching means and has an increased fastening power. 
     In the single-fin fastener provided in accordance with the present invention, an engaging fin has a flexible hinging butt at the tip of a support board projecting from a base member or the like and extends from the tip of the board in a direction opposite to that of the projection of the board. The engaging fin includes an engaging notched portion and a stopper extending therefrom to the movable tip of the engaging fin. The single-fin fastener is provided with an opening preventive portion extending continuously to the base member or the like and facing the stopper across a gap. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of the conventional single-fin fastener; 
     FIGS. 2A and 2B show sectional views of the conventional single-fin fastener in use; 
     FIG. 3 shows a perspective view of a single-fin fastener which is an embodiment of the present device; 
     FIG. 4 shows a sectional view of the single-fin fastener along a line IV--IV shown in FIG. 3; 
     FIG. 5 shows a sectional view of the single-fin fastener in use; 
     FIG. 6 shows a sectional view of the single-fin fastener being detached; 
     FIG. 7A shows a perspective view of a conventional single-fin fastener holding an electric wire; and 
     FIG. 7B shows a perspective view of the single-fin fastener of the present invention holding an electric wire. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described with reference to the accompanying drawings. 
     FIG. 3 shows a single-fin fastener B&#39; according to an embodiment of the present invention. The single-fin fastener B&#39; has the same basic constitution as the above-mentioned conventional single-fin fastener B with regard to a support board 1 on a base member A, a flexible butt 2 and an engaging fin 3, but is different from the latter with regard to an opening preventive portion 5 which is provided to prevent the engaging fin from being excessively opened. The opening preventive portion 5 is constituted by an inside part of the ring 5&#39; of the base member A, and faces the stopper 3b of the engaging fin 3 across a gap d as shown in FIG. 4. The single-fin fastener B&#39; is put in the hole 4 of the panel C so that the base member A is attached to the panel by the single-fin fastener. When a force F of 13 to 14 kg acts on the base member A in such a direction as to pull the single-fin fastener B&#39; out of the hole 4 of the panel C, the stopper 3b of the engaging fin 3 comes into contact with the opening preventive portion 5, as shown in FIG. 5, so that the force is borne by the contact P between the support board 1 and the inside surface of the base member A along the hole 4 thereof and the contact Q between the stopper and the opening preventive portion to prevent the engaging fin 3 from being further opened. The fastening power of the single-fin fastener B&#39; is thus increased. Besides, the base member A can easily be detached from the panel C by manipulating the stopper 3b of the engaging fin 3 of the fastener B&#39; with a finger as shown in FIG. 6. 
     Although the conventional single-fin fastener B has a drawback that an electric wire held by the fastener is located deep therein as shown in FIG. 7A, the single-fin fastener B&#39; does not have such a drawback. Electric wire entrainment preventing portions 6 of the opening preventive portion 5 of the ring 5 keep such an electric wire from being located deep in the fastener, as shown in FIG. 7B. For that reason, the single-fin fastener B&#39; is prevented from being damaged and is easily detached. 
     Although the opening preventive portion 5 is constituted by the inside part of the ring 5&#39; in the above-described embodiment, the present invention is not confined thereto but may be otherwise embodied so that a hole is made in the plate-like portion of a base member similar to the base member A and the inside surface of the base member along the hole is used as an opening preventive portion. 
     According to the present invention, a single-fin fastener is composed of a support board projecting from a base member or the like, and an engaging fin having a flexible hinging butt at the tip of the support board and extending from the butt in a direction opposite that of the projection of the support board. The engaging fin includes an engaging notched portion and a stopper extending therefrom to the movable tip of the fin. The single-fin fastener includes an opening preventive portion continuous to the base member or the like and facing the stopper across a gap. As a result, the fastening power of the single-fin fastener is tremendously increased.