Box Two Brake Post Extenders are the perfect solution for those riders in need of extra brake pad adjustment without switching frame sizes. CNC-machined from 6061-T6 aluminum, Box Two Brake Post Extenders easily mount to any frames existing cantilever brake bosses and provide an additional 16 mm of brake arm positioning. Typically, they are most useful when a rider transitions from one wheel size to the next (i.e. 451 to 406).