This replaces the two-part upper Z bar clamps on a Mendel and has vertical holes in it for you to attach supports for a spool holder. I just use a couple of Darwin corner brackets to hold the crossbar.Print, replace the pairs of upper Z bar clamps on your Mendel with these. Use a woodscrew to clamp the Z bar in place. Bolt vertical threaded supports into the vertical holes in the new Z bar clamps. Add a crosspiece using whatever bracketry you fancy (Mendel Y bar clamps are probably simplest http://www.thingiverse.com/thing:3843 ) and support your spool on the crosspiece.