Package comes with two size rubber ring inserts to provide a snug fit and protection of the mounting surface. The rubber ring diameter: 0.87(22mm), 1.0(25.4mm). You can add or remove them depending on the size of the handlebars. The handlebar clamp base diameter is 1.26 (32mm) when rubber ring insert is not included. The clamp base utilizes rubber insert & lock bolt to prevent loosening in high vibration for mounting to motorcycle & bike handlebars. Accommodates handlebars 0.87(22mm) , 1(25.4mm), 1.26(32mm) in diameters. Set also comes with an Allen key for easy installation.