Launched in 1999, the Pound Bumper Plates quickly became a top seller in training plates to the educational market. With the conversion from kilograms to pounds, it was a natural success. Each plate has two tongue grooves that run along the outer diameter of the plate, which allows the rubber to be molded to the inside of the plate. Nobody else offers these quality features.Plates sold individually, not in pairs.. 5 and 10lb plates are solid rubber, 25, 35, and 45lb plates are precision milled cast iron. Each plate sold separately, not in pairs