dummy - MGN12H and MGN12C carriages and MGN12 rail - LOWER POLYGON

MGN12H and MGN12C carriages and MGN12 rail
A remix of this thing https://www.thingiverse.com/thing:2051651, and this remix: https://www.thingiverse.com/thing:2794998

Polygon-reduced with 5 degree (on the C) and 10 degree (on the H) planar decimation. So that I can design around it without it completely slaying my system. (557,000 polygons is too many!)