Treadmill Doctor Proform 840 Treadmill Running Belt Model# PFTL721040 This is a 2-Ply Walking Belt for home or commercial use. If you have a fabric backing that is a different material than the top side of your walking belt, you have a 2-ply walking belt. Some sellers try to scare you into believing a 2-ply belt will harm your treadmill and that is incorrect. We have over 50yrs combined in the fitness repair industry and guarantee these belts to be safe for residential or commercial treadmills. Pre-Lubricated Extra Lube Included Lifetime Warranty Fasteners Included