Printrbot Maker's Upgrade Kit for 2013/2014 Printrbot Legacy Maker's Kits with Delrin Acme Nut, Includes Auto-Leveling Probe and GT2 Belts/Pulleys Update the Printrbot Simple Maker's Kits from 2013 and 2014 with Delrin acme nut (sold separately) to the Printrbot Simple Maker's Kit Model 1405 3D Printer Automatic leveling probe helps create a level print GT2 belts and aluminum pulley system facilitate more precise movement of the print head and bed than the original system Requires the use of a Printrbot Simple metal print bed and a Printrbot aluminum extruder (sold separately)