The followin link is a picture of the top mount on my newly constructed mini lehman, it is a 5/16" dia st/st ball bearing against a (used) tungsten carbide lathe tool insert. The ball sits in a steel washer soldered to two wire crimp connectors, with carbon fibre support wires for the boom. The bottom mount (at the end of the boom) is the same arrangement, and seems to work very well!.
             James
   
  http://www.freewebs.com/jridout/apps/photos/photo.jsp?photoID=7080079