RepRap Pro Ormerod Spring-loaded extruder

After problems with inconsistent filament diameters in my RepRapPro Ormerod I made an extruder block that includes a spring for tensioning.

It uses a long 3mm screw, nut and a tension string on a long lever arm. I've implemented this one with great results - it handles variations in filament with ease.

This works well with variable filament diameters. Smooths out the action of roughly printed gears. Makes cleaning the hobbed insert a snap - Undo the bottom spring screw, flip the back up and clean away! :)

As mentioned on forums.reprap.org it makes the mounting of iamburny's Herringbone gears (http://www.thingiverse.com/thing:242536) a bit easier because you can mount the gears separately, then mesh them together once complete.
The spring I've used came from a fairly strong action ball-point pen - the lever action increases the effect of the spring, so it works well for me and others.

####EDIT: Some discussion on the RepRap forums indicates that there is a large differenc