These extension tubes feature the 53x3mm 90° threads found on all screw-mounted GuerillaBeam parts. Their obvious use is for creating additional distance between projector parts.Their real purpose is to help you create your own lens adapters, light adapters, and/or accessories. You can remix the OpenJSCAD and/or recombine parts of it in your favourite 3d modeller. Some experience is required, but reading this, you can probably do it, and I'm always glad to help.Only for convenience I've included some (slightly older) STL files for common lengths. Instead, please use this OpenJSCAD for making custom lengths or edits. OpenJSCAD caveats:GuerillaBeam screw threads are optimized for 3d printing. This makes them much more robust than 'normal' 3d printed threads, but harder to model.Normally I use Autodesk Inventor, but I wanted to also share the Design in a FOSS-compatible format, preferably OpenSCAD.I didn't manage to recreate them in OpenSCAD though, so I went for OpenJSCAD. OpenJSCAD is easy when you know OpenSCAD and Javascript. In any case, you can use the OpenJSCAD to generate a 3d model that you can reuse in your favourite 3d program.Tip: If designing screw threads, add them (union), don't 'cut' them (difference). It's easier math, and your CAD program will thank it to you.I've additionally incorporated a primitive text stamp, so that every extension tube gets it's length engraved (optional).You can find most GuerillaBeam parts here on Thingiverse, tagged with GuerillaBeam.