My understanding is that the GWS Slow Stick comes with a "prop adapter" (set screw of adapter can barely be seen in the left picture). Depending upon the prop source, you may need to ream or drill out the prop hole until it fits the adapter shaft.

To protect the prop from damage, many flyers use "prop savers" instead (in right picture shown without rubber band or o-ring). Again, the prop may need to be reamed or drilled. The prop saver holds the prop with a rubber band giving an elastic property to the mounting.

Rick