Robo3D Z Isolator v2 (with nylon nut)

#### Description
This design works a lot better as the surface of the nylon nut's washer face slips on the X carriage much better and the nylon nut has less slop on the threaded rod and less stiction. It helps remove Z ribbing caused by bent Z screws and/or Z couplers that aren't perfectly centered. Works best in tandem with a Z constraint like http://www.thingiverse.com/thing:1124184

#### Instructions
This design requires M8 Nylon Washer Faced nuts with a 13mm face to face distance. Such a