When using a folding propeller with a pusher aircraft, it's critical to have a prop-stopper to prevent the blades from folding back past center when the motor is stopped. If you don't have one, the blades can cross and will then cause an imbalance so bad it will rip the motor off of the plane when you start it back up.
This device solves that problem and also prevents the blades from snapping forward too far on start which can (depending on the aircraft design) cause damage to the plane.
This updated version is a fully-parameterized Fusion 360 model. You can customize it for any spinner you'd like just by changing parameters. I've included 4 sets of parameter files, and the .STL files generated by those.
They are for the MPI PK50 and PK40 and the TopModel 36mm and 32mm spinners.
One location to buy each of those types is:
The PK50 version was tuned to work with Aero-naut CAM folding blades in the 13 inch range.
The BB version was tuned for 10-12 inch blades.
Other sizes may work.
Fusion 360 design and .CSVs with the parameters are included. The Fusion 360 plug-in "ParameterIO" can directly read them for import.