This is the green belting that covers the slot in the middle of Polar, Itoh, and other cutters. Equivalent to Heidelberg part #3231113. This belting is available by the foot, but this particular item in stock is already cut to 2.2 meters (7" 2³⁹⁄_64" to be exact). It comes with a guide in the middle running the length of one side.

The type of belting comes in different sizes depending on the machine model and serial #. It could be 60mm wide with a 10mm x 6mm belt on the underside, for example, and a guide, or could be 39mm (roughly 1.5") wide without a guide.