Monocoque body, custom alloy, fully articulating head, absolute length markings, proven easy to use adjustment collars, positive snap-in skinny adapter, modern bend curve, etc. Pro 1 Alloy booms have exceptional torsional rigidity and fit both standard and reduced diameter masts perfectly. The addition of absolute length markings on a generous 62cm tail-piece aids with rigging your sail properly. The rounded front bends of the 135, 150, and 165 models make hand transitions during jibes, tacks, and the most advanced freestyle moves feel natural. Grip Diameter: 29mm - 1 1/8".