Andersen&reg; Gliding Patio Door Tandem Roller Assembly For 8' Panel Andersen Gliding Patio Door Tandem Roller Assembly with Bracket for 8' Panel Works w/ 200 Series Narroline, 200 Series Perma-Shield and 400 Series Frenchwood Gliding Patio Doors Dual ball bearing rollers on bottom of the operating door panels provide smooth gliding operation Self-contained leveling adjusters We recommend replacing both rollers at the same time