All my direct thread on fixed barrel experience is with the Griffin taper mounts. The Omega 9K components sold separately have me confused. For a Glock it is clear I need mount/piston/spring. But for direct thread on an AR (300BLK & 9mm) do I just use the mount alone? Do I need the fixed spacer too? Or is the fixed spacer only to be used with piston for a fixed barrel sub-gun?

Pic of parts:
Attachment 4848