Here is a simple design for a bearing mount that can be used to hold an 8mm lead screw or 8mm guide rod. I have been kicking around the design for a DIY CNC mill table using the Gen 3 MakerBot/RepRap motherboard and stepper driver cards.The object accepts the 608 skateboard ball bearing and there are 2 mounting holes for 3mm or 4mm bolts to fasten the thing down.I am beginning to enjoy using an HBP to run ABS raftless, and printing this object without one worked fine. INFILL DENSITY in the SkeinForge FILL menu was set to 0.3 for my copies but may be set higher depending upon the user's end application. There is not a lot of work to do on these after printing - Scrape out the bearing opening of excess plastic then press fit the ball bearing in. The fit is tight, but you can carefully add a drop of superglue between the mount and outer rim of the bearing if desired. The 2 block mounting holes might need a small amount to material removed from the holes, but I just pushed 3mm bolts through to take care of that when fastening the mount down. Sanding with 220A gives the object a better look, but it will work fine without sanding. Use flat washers or cap headed bolts for mounting to increase the surface area holding the block. A small headed bolt would put all kinds of stress on the mounting holes when tightened.