Idler Pulley Plate The Idler Pulley Plate is designed to be used with both V-Slot Linear Rail and OpenRail Linear Rail. "The idea behind this plate is to give you a mountable yet movable plate for your Smooth Idler Pulley. This works great as it allows you to easily tension your belt." Product Details Qty. 1 Version - V1 6061 - T5 Plate 3mm Thick Anodized Aluminum Color: Black Application: