1" (25.4mm) outer diameter, takes 1" (25.4mm) inside diameter handlebar grip. Allows using handlebar grips as footpegs. OFC (Ost Freesen Choppers) designed these as lightweight CNC machined billet aluminum footpegs with a plain peg surface. Simply installs to the bike as a regular footpeg and then allows you to install any regular handlebar grip over the footpeg adapter's plain surface. Perfect for style matching the footpegs to the grips. Fits all 'H-D traditional male mount' style footpeg mounts.