This part has been developed by Brompton for strengthening pre September 1999 Modal handlebars. It can be used also to mount parts like bike computers, GPS devices, lights and attach a small bag or whatever you like and works for you...it's made of glass fiber reinforced plastic and stainless steel hardware. There are two sizes, for handlebars with 22,2 mm diameter tube and for the old polished handlebars with 23.5mm diameter tube. The latter is recommended to be replaced for your safety unless your vintage Brompton is being treated as a museum piece and should be kept in original condition.