Chinese brand Iwalker is making liquid fuelled stoves since a few years. They also have a range of spare parts and additional option available for there stoves. Among them are small silent caps that can be used as a replacement for a roarer burner cap. Main difference is the threading that is used to screw it on top of a stove. They supply them with M10 x 1,0 and M12 x 0,75. Besides that they also have two different materials of which they make the silent cap itself; brass and carbon steel.
The M10 x 1,0 fits perfect on a Primus 71 or a SVEA 123 (not R). The M12 x 0,75 fits on a Russian PT-1 stove. All are small self pressurising (no pump) stoves. Unfortunately the famous Optimus 8R and SVEA 123R use a threading that is slightly different.