This thing allows you to precisely position and align the 45 degree secondary mirror on a Newtonian telescope.It is designed around a 1 inch (minor axis) mirror, but you could conceivably use a much larger mirror.The facets on the mirror holder sides make it easy to adjust it's alignment Nov 4 '11- I updated the files for three changesThe center screw is an M4 of some length. The collimation screws are M3 of some length. The M3 have to be sized lengthwise in relation to the M4. Also, I guess they shouldn't be too long, since they might bend. Adding springs somewhere makes it a bit easier to align.The spider is held in the center of the optical tube with 3 vanes of 3mm threaded rod. buy 1 meter and cut to the size you need. Maybe you can use wire, if you can't get M3, but i think you'll have too much vibration.Once the spider is in place in the scope, you can fill the cavity (with the m3 nut and vane ends) with epoxy or glue. This will keep them aligned 120 degrees opposed, and will also lock the nuts in place so they don't rotate.