Extension tube set (20mm/40mm/60mm) for Canon EF mount.
Extension tubes are used to allow a lens to focus closer than it does natively. This is accomplished by moving the lens farther away from the camera body's sensor plane by fitting between the camera body and the lens. The end result of focusing closer is a larger magnification.
Tubes have rippled surface for easy mounting and very tightly fit to lens and body mount.
If you aren't satisfied with the size of the tubes, you can customize them for yourself.
I added a python script that generates a file with the openscad tube model. The script uses opyscad library from https://github.com/SkyRzn/opyscad. Save canon_ef_extension_tube.py and opyscad.py in the same directory and run canon_ef_extension_tube.py in the python interpreter.
0.2mm layer thickness
0.5mm extrusion width
3 solid layer
3 perimeter loops