The external cap (C) snaps into the base component and evenly tightens the screen, completing the installation. When rescreening, the cap temporarily pops off, allowing a quick and efficient replacement. Made of UV-resistant window grade vinyl. Never needs painting. 8' lengths. All 1-1/2" wide caps. Base attaches to a 2x4 or 4x4 wooden frame. Screen spline rolls into the spline groove. Cap snaps onto base. Screen-Tight recommends fiberglass screen (including sunscreen).