This belt came from a functional 600s treadmill.  I do not know how old it is or how many miles it has on it, but I walked on it and it was fine. 

According to FitnessRepairParts.com, it is a replacement part for these machines:

Gold's Gym

Good Family F900 - GFTL088040

Good Family F900 - GFTL088041

Proform

570 V - PETL513050
570V - PETL513052
6.0 GSX - PFTL511050
6.0 GSX - PFTL511051
6.0 GSX - PFTL511052

6.0 GSX - PFTL511053
600 S - PFTL521050
600 S - PFTL521051
650 Cross Trainer - PFTL598060


Please write with any questions.  Have a great day. Aloha!