I created this based on someone's else design here http://forums.reprap.org/read.php?406,484958,507546#msg-507546. This is just an extruder mount to make the mk8 compatible with j-head groove mount also compatible with the link to the original design. The original design were off to the right by the designer because he wanted to have the motor rest on the hot end mount but I don't prefer that because I would lose some print volumes by about 5-10mm (which isn't that great to be honest). So I just trace along all the lines and recreated another that sits at the center (slightly to the left of original mk8 mount position by about 3-5mm) so that I don't have to mess with the printable area for x axis. For this, you just have to take out the existing fan and heatsink and reuse the longer screw again As of now, this design would remain as experimental until I get my e3d although I already have all metal j-head, but keep changing hot ends would require a lot of calibration and rewiring to be done. But this item should work fine. I only redesigned the groove mount for mk8 extruder compatible. The e3v lock and x carriage are not my design, I take no credits in these 2 item Anyone who are going to print this item and tested it, please let me know in comments below so I could make some changes or something Also,, this uses 25mm length lm8uu v2 available here http://www.thingiverse.com/thing:893941 v3 here http://www.thingiverse.com/thing:905619Print along the carriage if you are planning to use long hot ends like j-head or e3d because mounting the mount on original geeetech carriage would give you lesser z axis print volume or if you don't mind, can use the extruder mount on existing geeetech carriage as well except the hot end would stick out more than the original hot end