These are good scale-like props for other parkflyer size aircraft. Very light for their size, and flexible. They don't have adapter rings, but a hexagonal cavity in the back about 10mm across, and a 4.5mm hole in the front. Mine needed a little bit of balancing. They seem quite efficient when tested on a wattmeter, and spin much faster that an equivalent APCe clone (most likely due to their very thin blades). I'm running about 130W through mine and they don't seem to be distorting much (14K RPM). IMHO they would be OK to about 150~160W, I wouldn't push them further than that.