N6539 Mounts into 1" wide style bi-fold door tracks, two-way spring snugger, when opening or closing. Used on Acme, Stanley and other door systems. Features: -Door top guide. -Material: Nylon. -Door thickness: 1" to 1.38". -Mount: Top. -Spring loaded: Yes. -Dimensions: 7.44" H x 3.81" W x 1.13" D. Installation