Adjustable 8mm linear bearing

Concept design of an adjustable linear bearing to suit 8 mm OD linear rail
Id had a few issues on my old original Mendel machine where the 8mm smooth rods are not very good quality and the diameter tolerance isnt very good. Add a couple of years of wear and the standard LMU8's were noisy and loose so i have designed this.
I have printed this with Esun's PLA + filament as it is as easy to print as PLA but has the characteristics of ABS and should suit this application well.
Im using WD40's PTFE "dry lube" spray http://wd40specialist.com/products/dry-lube/

Y axis bearing holders to suit this 16mm OD can be found here > http://www.thingiverse.com/thing:1435072