UPDATE 20.8.2014: Added GT2 belt clamps. These clamps provide NO tension, so they will work with 303 tooth GT2 based setups. Note that if they seem thin for you, you can always just scale them up a bit in Z if that seems necessary. UPDATE 26.12.2013: The parts that engage the endstops have been widened to 10 mm to compensate for the blocks being 2mm wider towards the center of the printer, so that the default endswitch positions still work. All the files have been updated accordingly.I love experimenting with my Ultimaker. Unfortunately when you want to do that with different extruders (like non-bowden ones) or printheads, you must disassemble a lot of things and it takes too much time. Not any more. These blocks allow you to switch printheads by removing 8 easily accessible bolts (leaving everything else in place) and twisting the print head to remove it together with the 6mm rods. They also increase the rigidity of your whole XY stage, and provide decent belt tension. You can find detailed instructions here: http://chopmeister.blogspot.com/2013/12/twisterblocks.html