Stanley Hardware S837-526 V391GR Folding Door Part in Zinc plated Authorized Replacement from National Hardware Stock #N344-911 Guide rollers stay in the track and adjust to door frames that are not square Ensures smooth operation Manufactured with cold-rolled steel and nylon Manufactured with cold-rolled steel and nylon Guide rollers stay in the track and adjust to door frames that are not square Ensures smooth operation LifeSpan Limited Lifetime Warranty Weather Guard finish for superior corrosion resistance