Find enclose some more pics of the device. as you can see the stack is finished by a rounded lip that fits exactly into the last rounded furrow inside the filter. This way only the filter rubber pressure is require to keep it in place. I can take it of by hand but it´s secure enough not to lose it in flight (never since I did it six months ago)
Of course it is easier to buy from VARIO the plastic mount (with or without choke) but the air filter and the carb are not aligned and that makes lot of turbulences before the carb. not nice
See also an example of my plug state after several flights (always at a 4% oil mix). No residues. The engine is making a good combustion helped imo by a fine fuel dispersion even at high oil %.
This summer we flight at 107 º F weather temp and the engine never goes over 230º F after five mins hovering (188ºF after a FF flight)
PD the engine is a G230RC with a 26cc cylinder and the air filter the same supplied by VARIO as spare