As the 2BEIGH3 Printer is a large unit, there are times when I want to take advantage of very small nozzle sizes. To do so, I designed a 2:1 gear reduction system that uses the standard mounting holes. A second requirement was to maintain the belt path. To accomplish this, two idlers are used. The Belt System for the 2BEIGH3 is the XL 3/8" .200" style. Operation is best demonstrated in a video: https://www.youtube.com/watch?v=pD0TGcQcKG0&feature=plcpThese are printed in 618 nylon, therefore they need no bearings. Instead, stainless steel "Partially Threaded metric bolts" are used. While nylon is pliable in thin parts, after about 5-6 solid layers, it becomes very strong. The pliability is used to maintain a friction fit of the drive gear, while the slippery properties are used in the main belt drive and idlers. The gears are ever so slightly oversized to maintain a constant mechanical mesh to eliminate any backlash. The belt drive 8 T XL comes from http://www.thingiverse.com/thing:16627 The XL drives are a bit long, so you can cut to a needed length.Print: 2-3 perimeters depending on your current nozzle size. 3 solid surfaces 60%-90% fill For holes, we use "inch" sizes just over or just under the required metric size. This gives a tight friction fit of the drive gear, as well as just enough clearance on the idlers. The lengths of bolts required depend on your stepper mounting flange thickness. You'll need to update your steps/mm in software or the part will be 50% of design DIM.