This design uses 3 lengths of 20mm x 20mm aluminum extrusion and a bunch of printed parts to form the telescope tube for a Printonian telescope.Specifically, it uses 80/20 extrusion, and I don't know if the tolerances are right yet, so consider it a work in progress.You will need 3 Primary Ribs, 4 Secondary Ribs, 2 Ribs (just plain old ribs), and a Focuser Base. If those alone don't provide enough stiffness, add Rib pieces until you are happy. More ribs will help with keeping a cylindrical shape if you want to wrap the tube with something. It's a good idea in order to keep dist and things off the primary mirror. You can also line the inside with black felt to keep out stray reflections. The pieces are held in place with 3mm cap screws in self tapping holes, so don't torque the screws down too tight or they will strip and you'll need to print again (or use glue).The length of your extrusion pieces will depend on your primary mirror's focal length and diameter, but assuming it's a 114 mm mirror and 900mm focal length, you'll need three ~1 m lengths.