These silencers are designed specifically to fit into AdrenalinR motorcycle mufflers. The sizes referred to are the silencer tube diameters. The smaller the diameter, the quieter it is – BUT the smaller the diameter, the more restrictive it is also.
They take the edge of the sound, especially on single cylinders.
There is a bit of fitting required, the holes will need to be drilled to bolt in the silencer. We recommend a 5mm diameter drill bit