Fastening device for flexible sheets

Claim 1

A fastener for clamping a portion of a flexible sheet, comprising: (a) a pair of resilient heads for receiving therebetween said portion of said sheet; (b) one of said heads having along one side thereof a lug with spaced front and rear locking lobes extending transversely of said one of said heads, said lobes extending toward the other of said heads and diverging from each other in the direction in which they extend, said lobes having convex surfaces; (c) the other of said heads having front and rear flanges extending transversely of said head, said flanges having spaced opposed concave inner surfaces conforming generally to the outer portions of the convex surfaces of said locking lobes; (d) said other of said heads defining, between said flanges, an inwardly opening recess for receiving between said flanges said portion of said sheet and said locking lobes, with said front flange extending partially around a portion of said front lobe and said rear flange extending partially around a portion of said rear lobe; (e) one of said heads having a transverse valley between said front and rear lobes and the other of said heads has a central lobe within said recess, said central lobe being between and spaced from said flanges and protuding to a lesser extent than the extent of the flanges into said valley of one of said heads, when said lobes are received in said recess; (f) said front flange extending sufficiently around the front portion of said front lobe, and said front lobe extending into said recess sufficiently that when said portion of said sheet and both of said lobes are fully within said recess, tension applied forwardly on said sheet will not readily force said lug out of said recess; and (g) said front lobe being confined by said front flange to a greater extent than the rear lobe is confined by said rear flange so that said heads can be urged apart by urging the rear portion of said one of said heads away from the rear portion of the other of said heads as the front portion of one of said heads pivots about the front portion of the other of said heads for releasing said lug from said recess, and said lug cannot be readily removed from the other of said heads by without first removing the said rear lobe from said recess.