I just bought a Master Airscrew 12 in folding prop and looked at the insides. How does it attach? Is there an adapter for the metal bar holding the props? I just do not see how it will fit.
Bill R.

On my MA folders, there's an 1/8" diameter hole in the center of the connecting bar that fits on the prop shaft...
You may need some manner of adapter to use this prop.

Yep, it's intended to be used with a conventional prop screw type adapter. It's not meant to do directly onto a simple shaft. As I recall mine there's not enough meat there to drill and tap for a set screw even if your shaft is the correct snug fit in the hole.