This insert style sliding screen door assembly has a high density polyethylene housing with a high density polyethylene roller insert. It is used on the Academy Uni-Fit screen doors. The roller is a 1 in. high density polyethylene roller and is used on the top or the bottom of the door. Easy to install by inserting into the open U-shaped frame and inserting the screw. For steel ball bearing see Prime-Line part B 624.