The Kupo Arch Coupler with 28mm Spigot is a lightweight and low-profile professional coupler constructed from high-tensile aluminum and steel alloy. It has been developed for installations where load capacities of up to 330lbs (150kg) are required. Kupo professional couplers combine strength and durability with a high degree of safety. This type is designed to fit tubes with diameters between 38mm-51mm (1.5in-2.0in).