Self locking seam forming members

Claim 1

A pair of continuous inter-engaging seam-forming members extruded from plastic material, said seam-forming members being of the same J-shape in cross section and each including a stem portion integral with one edge of a crescent shaped trough portion, the trough portions of said seam forming members being interlockable when overlapped with their open sides facing toward one another, the free lip edge of each trough shaped portion being engageable with the interior surface of the trough portion of the other seam forming member generally in the plane of the stem portion thereof, said stem portion being relatively wide thin and flexible, said trough shaped portion having a relatively non-flexible mid-portion several times thicker than said stem portion and with the opposed sidewalls of said trough shaped portion converging from said thick mid-portion to provide a relatively thin entrance lip edge and the other sidewalls tapering into a merger with said relatively thin stem portion, and the stem portions of said seam forming members lying generally in a common plane passing between said free lip edges of said trough shaped portions when said seam forming members are assembled and under tension load crosswise of the seam.