The HERCULES Ukulele Clamp USP20CB features the Auto Grip System (AGS) yoke and the fully adjustable clamp that can be attached to round, square tube and desk. The built-in Auto Grip System safely locks the instrument in place. It can accommodate ukuleles of all sizes from soprano to baritone ukuleles. The Fully Adjustable Clamp can be attached to any tube or desk within the following dimensions:15.8 mm - 30 mm (0.62" - 1.18") round tube18 mm - 25.4 mm (0.7" - 1") square tube10 mm - 25 mm (0.39"