Hey thanks for replying, I had kinda of given up hope and was getting ready to tear into the printer. The printer has been turning out some good prints except for some horrible ringing. I wanted to do these upgrades to tighten up the machine and hopefully get some high quality prints. My first printer is a davinci duo which is all brass bushings so I have had no experience with linear bearings. I thought 4 rows of balls to be too little and would cause excessive wear and unwanted motion. To my mind 6 or 8 rows seemed to be more precise, but if 4 rows is standard I will go ahead and order the Vxb's.