RDG stands for Reduced Diameter Grip. This is a new model for 2017. We've reduced the grip diameter another 2mm from our standard small diameter Pro-1 Alloy Booms. To accomplish this yet retain the durability and stiffness our Alloy booms are known for, we use a special tapered tube. This allows us to use our new Fiber Composite 2-Pin Adjusting Collars and proven continuous tail-piece, providing stiffness and durability you expect from Chinook. Partly due to the alloy tubing and also a slightly reduced adjustment range, the boom is lighter than other non-tapered booms on the market. The addition of absolute length markings on a 60cm tail-piece aid with rigging your sail properly. Exceptional torsional rigidity and fits both standard and reduced diameter masts perfectly. One year warranty.