I needed a block and tackle to lift hay bales in my shed. I found this one here by Mysabre73: http://www.thingiverse.com/thing:963214 but it was too big for my 150x150 Printrbot Simple. I got it printed at 90% but figured I'd rather have 608 bearings on the pulleys so it ran a little more freely and lasted longer. So I whipped up some OpenSCAD files and got it done. Update 1: I found out how to join circles by tangents rather than direct to a perpendicular radius. Version 2 of the .scad and .stl files use the 'hull' function. I haven't printed this version yet, but it should be neater.I sliced all STL files with Slic3r, using 4 shells and the new 3D honeycomb infill at 30% for strength. The long parts must be rotated 45 degrees if you only have a 150mm (6 inch) bed. The bolts I used are 6mm x 50mm high tensile. The holes in the shells and the 608 bearings have an ID of 7mm so I used a 1mm sleeve to make it snug. A 1/4 x 2 inch bolt may work for the imperialists. 6mm abrasion resistant rope finished it off.