These are a set of mufflers for the heated air intake, the combustion air intake, and a capsule to deaden the sound of the fuel pump, to be filled with insulation of your choice. the caps have an offset hole in them to aid in getting the appropriate tilt of the pump inside by spinning them 180 degrees from each other. Walls on the cylinder are 12mm thick with infill that looked like it would reflect and scatter sound best, who knows. I printed these in PLA pro but they do not naturally encounter heat so use something that will not get brittle with time and that's all you need for a normal application. I sized this for a 2kw 60mm hose.