08/07/2013 - This has been superseded by Version 2 of the extruder calibration tool found here: http://www.thingiverse.com/thing:114614 This is a tool I designed to help with the calibration of the extruder on the Felix Printer. I was frustrated with inaccuracy of marking filament and trying to measure with my callipers. This helps by providing two flat surfaces that the vernier callipers can easily measure between. It is simple to install and remove without having to remove any filament from the extruder. Just push the filament into the top piece and start the calibration process as per normal, measuring between the top and bottom as you go. There are still a couple of things I still need to fix on this design, but works as is. It is designed for 1.75mm filament and has a very tight fit so may need some adjustment by filing the push fit until a snug fit for the filament is is achieved until I fix this problem. This was designed for the Felix v2 Printer (http://www.felixprinters.com) but should work with an other model printer.You will need to add support when printing, it's minimal.