There are four key components that make up a synchronous belt. -------Tensile Cords/Backing/Teeth/Tooth Facing.

1: Tensile Cords: Resistancing to elongation.

2: Backing: Avoiding the tensile member from oil, moisture ect.

3: Teeth: Perfom the function of fitting the grooves on the pulley or sprocket. (ZA, ZB, ZBS, ZH, YH, ZS, S8M, RU, MR, MY, YU, etc. )

4: Tooth Facing: A wear-resistant nylon fabric that can protect the teeth and keep frictional loss to a minimum.

Timing Belt is a most important parts to your engine, A bad one could damage the other related parts even to change the whole engine. Please do sell the good one!