A Slide on / off nema 17 box with a screw hole for long screws.This is for lowering your Z end stop for head attachments that go below the current Z end stop.The longer screw reaches the switch from higher up.It slides on and off easily at any time. It has a fan mount on top aimed at the extrusion head, useful for helping cool the extruder motor or as an area cooler. If its put on with the fan on the bed side, it blows down onto the bed.(see derivitive sorce) Intended for use with these:PrintRbot laser mount thingiverse.com/thing:30064PrintRbot engraver mount thingiverse.com/thing:30520PrintRbot marker mount thingiverse.com/thing:30999PrintRbot Z end stop extender. http://www.thingiverse.com/thing:30590