This is the next iteration in the design of an extruder calibration tool I use 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. This was designed for the Felix v2 Printer (http://www.felixprinters.com) but should work with any other model of extruder/printer. Please let me know of anyway you see this can be improved.The base requires support when printing