Allows you to adjust the tension on your x-axis belt by turning screws. A belt clip is used instead of zip ties to retain the ends of the belt.
1) Remove the x-axis belt ends from the extruder carriage.
2) Place the casing onto the extruder carriage so that the belt pass-through hole aligns with the one in the carriage.
3) Route the x-axis belt ends up through the carriage/casing assembly.
4) Open up the screw holes on the insert with a 5/32" drill. Insert a 3/4" 6-32 bole through the hole and attach a matching nut on the bolt. Snug the nut down so that it seats into the hex nut recess in the insert.
5) Remove the 6-32 screws for now.
6) Place the insert into the casing and feed the x-axis belt ends though the insert and pull it snug. Push the insert all the way into the casing until it rests on the bottom.
7) Pull the x-axis belt a tight as you feel comfortable doing. Slide on the belt clip as low as possible.
8) Reinstall the 6-32 screws. Adjust the belt tension so that it is the proper tightness... nice and snug but not so tight as to put excessive strain on the system components, or to stall the x-axis stepper motor. Somewhere around 1/4" deflection on the belt before you're really tugging on it.
*Most of the verbage is rickmellor. Thanks Rick!