Our motorcycle mirror stem mounting attachment is designed to fit on mirrors / crossbars / fairing bars with a diameter of 8-16mm. This attachment is designed with the 25mm / 1" ball head which can be used with a wide range of adapters. This attachments is very popular not just with motorcycles but also scooters where their handlebars are hidden with plastics / fairings. Options include the Ultimateaddons version 2 of the 25mm to 3 prong adapter is one of our most popular adapters to fit a wide range of 1" / 25mm ball mounts. Please select the option if you wish to include this adapter.