
Elgato Multi Mount Solid Arm
Various video accessories
Elgato Multi Mount Solid Arm
Various video accessories
Your hints are a bit confusing. I don't have a Smallrig clamp or an Ergotron post, but I do have several Smallrig camera cages, for example, and the arm fits perfectly in all the holes. I can also screw on a Ballhead from Ulanzi or Joby or any camera body. Perhaps the thread on yours has a fault or some burrs.
Then you have two balls😉 I.e. yes but only conditionally recommended. Tends to be suitable only for light equipment.
No, it is not available in a shorter version, but in different extensions. All products including detailed specifications are available at elgato.com.