This unit is all printed without brim or supports.  For added strength I usually print with extra perimeters.  I use PLA for strength.

The outer groove of the bearing and the relief in the block should allow up to 10mm (3/8") rope to be used without interference.

The bearing uses 6mm balls that are available as Airsoft BBs.  Bearing rotates very easily just like a commercial ball bearing.  The bearing unit is built in 4 parts to allow ball placement after printing.  12 or 13 balls can be used.  Depending on printer settings and filament differences you may want to experiment with the number of balls.  It is suggested that the bearing be printed at .15mm layer height for smoothness.  The halves of the inner and outer races are joined using a tapered tongue and groove interference fit and will require some force to join together so glue is not required.  When properly seated there should be no appreciable gap visible between race halves.  

2 washers should be printed and placed between the bearing and the block itself.

The block can be printed at .2mm layer height.

Use a 6-32 or equivalent bolt and nut as an axle.  If the hole is too tight, slightly enlarge the hole with a 9/64 drill or use the threads of the screw to ream out the hole.

Bearing assembly

1. Connect both halves of the inner race together tightly.  A hammer or vise may be used to close the gap.
2. Lay one half of the outer race on a flat surface and roughly center the completed inner race inside.  
3. Add 12 or 13 balls.  The balls may have to be lightly pushed into the groove.  
4. Connect the other half of the outer race tightly.  A hammer or vise may be used to close the gap.