RE: Hangar 9 33% Edge 540
Bill,
That's a good question.
They appear to be very strong so I decided to initally use them as they came from Kohler/Actro for this purpose. They also make installation easy on a 1/4" or 5/8" plywood firewall using M4 nuts and t-nuts.
I mounted my 20x10 APC e-prop and 4" CBA spinner this morning so i'll post some pictures soon. After I get the landing gear installed, I'll start my power testing. One of the tests will be to see if the rubber mounts have any ill effect.