If I counted correctly, eight marbles (9.5mm or 3/8" ball bearings) were on the track. Works great with 1 to 8 marbles at 1.5vdc, and 1 to 12 marbles at 3vdc (although at the higher voltage, you may loose your marbles). Uses the base assembly ("Base.stl", "Gear Crown.stl", "Gear Motor.stl" and "Gear Worm.stl") from the original Marblevator "Mini", Bowl Edition. If you've already built the Marblevator "Mini", Bowl Edition then simply push out the worm gear and track, then install this track assembly and replace the worm gear; takes about 20 seconds or so. If not, build the Marblevator "Mini", Bowl Edition first. Prints in two pieces that are snapped together. And finally, if you don't mind manual labor, the hand cranked version is available. Printed in PLA on a Makerbot Replicator 2 using Makerware 188.8.131.52 "Standard" settings.
Print the two pieces, press together, then install on your Marblevator "Mini" base. The press points are a tight fit, so some trimming may be necessary depending on your printer, printer settings, and colors.