About this 3D model

made for my next enlarged rostock http://www.thingiverse.com/thing:80472 the carriage is here http://www.thingiverse.com/thing:139264 but with correct mesures (magnet are 13mm X 4.6) this is the correct magnet (The one i used) http://www.ebay.it/itm/Super-Magnete-al-Neodimio-CSN-13-POTENZA-3-Kg-FORO-SVASATO-BASE-IN-ACCIAIO-/400535138240?pt=Monete_Italiane_in_Lire&hash=item5d41c12fc0 and these are the balls http://www.ebay.it/itm/261115915534?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2648