Made of steel, allows you to focus indefinitely.
This adapter is intended for use with some M42 mount lenses with an outer diameter of about 51.00 mm and a depth of this part of 8.20 mm on cameras with Arri PL mount.
This way you can install any lens that is narrow enough at the back - less than 51.00 mm in diameter.
All 4 bayonet tips have cutouts to provide 4 mounting positions (for example, you can place the index mark of the lens to the other side for the assistant to work).
 
Weight - 60 g.