This secondary holder has a unique feature I haven't seen anywhere else (if you have, please
mail me a note). When collimating, the secondary stays centered in the optical tube assemly.
This is achieved by mounting the secondary between two spherical surfaces 2 and 3 whose
center point coincides with the calculated offset point at secondary surface. So the
offset point stays at the optical axis of the telescope.To collimate, just grab the secondary with one hand, make loose the nut 4 and adjust. I've found this easy enough, so I don't need any fine adjustment screws.
To scale the drawind minor diameter of the secondary is 90 mm (3.5") and spider vanes 6 mm (1/4") dia steel rod.