High Tensile Aluminium. Various Sizes. Wing Nut & Bolt Fixing. Black Or Silver FinishSWL: 100 kg (all sizes) Widths and fixing: T58887: 21mm M6 fixing T58830: 30mm M6 fixing T58997: 30mm M10 fixing. The Atom Hook Clamp Couplers are supplied with a Wing Nut and Bolt Fixing. (Not Shown on the silver picture). Manufactured from high tensile aluminium extrusion. The clamps are available in sizes to fit 25-32 & 38mm diameter tubes.. clamp-doughty hook clamp-truss hook clamp-coupler clamp