These curtain tabs are used in vintage trailers from the 1960s and other eras. These sew in to the edge of the curtain. The wide part goes in an aluminum track.
Tabs are 7/8" wide and 3/4" tall. The bulge that goes in the track is 3/16" wide. The flat pliable plastic sewing surface is 1/20" thick, so you will need to use a reasonably strong machine to sew through them.
Package of 14.