Below is a list of Round Belts manufacturers from Portland, Maine. Round belts, also called o-ring belts, are round elastic bands that connect the outside edges of wide flat belts to the chains along a curved conveying line. They prevent the flat beds from slipping inwards. They are referred to as endless because, like o-rings, they are made of a single piece of stretchy, elastomeric material, usually plastics like polyurethane or silicone, and do not have a splice or seam.