This is how the bearings are made. A lathe and a drillpress was used. The hole is made about 100 thousandths larger than the boom where it mounts. Since the mounting is on two different boom sections, one bearing has a smaller hole than the other, and is further from the bottom of the clamp point so as to keep the antenna horizontal to the gusset plate.
These are early prototypes of the bearings. The final ones were made from hardwood (Yellow Pine), and were painted.
Below are two views of the clamping collars that are used to keep the antennas from sliding through the bearings.