The R-series is available in two mirror sizes, a 35mm and a 50mm diameter. They both provide a very similar view but the smaller mirror is more challenging to use, a tradeoff for the sake of minimal form. They consider the R35 their "pro" (vanity) mirror and the R50 our touring model.
Not compatible with extreme bar geometries or positions. Some Enve bars and others without standard bar plugs also may not work. Email photos of your setup if you have any questions.