Might be of interest to some of us still playing in the mud with the 1st incarnation of the uni track. This is an experimental arm off one of my bikes. I had the centre machined out to take two 6002 sealed bearings and a 1mm inner sleeve made to suit the 14mm bolt.
It will be going on to a practice bike and given a lot of abuse to see if it is up to it.
If it works then I'll make up some ally arms that are opened out to the bearing size and maybe then find some 15mm bolts to negate the need for a shim. :-)