MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.

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I just re-measured the STL file with Meshlab, and the idler block holes come out at 4 mm diameter for me. The old Darwin I use to make these has slowish Gcode processing, and always makes the holes a bit undersized, so I habitually drill them out before use anyway, but slightly larger holes wouldn't hurt.