I have them here with me at work, and they are threaded. These were for a Phantom 2, my son has a P3 standard, I'm pretty sure they'll fit his. I was just curious if they might fit mine. I'll just find out when I get home. If they fit, then I've got an extra set of props, if not I'll give them to him.
Phantom 2 & Phantom 3 props will "fit". P2 have a metal hub, P3 have a plastic hub. The plastic hub is for the braking system that was introduced with the P3 series.
Props are cheap. I would stick to the Autel props. I have never seen the need to use anything other than the OEM propulsion system (props, batteries & motors).
I personally have never needed to purchase additional props for my DJI or Autel aircraft. If you don't damage them in a crash they will last a long, long time.