For use with Avery DTR Eco letter trays, these risers are made from durable, high impact polystyrene and allow you to stack trays, providing additional, space saving storage on your desk or work space. The 8mm diameter risers insert easily onto each corner of the letter tray, which can be stacked straight, staggered, in reverse or at a 90 degree angle. This pack contains 4 black 75mm risers.