Yes, in order to mount the ball nut properly, it needs to be removed, turned upside down and re-installed. If you do that you will have a mess of balls all over unless you use the item I linked to to keep the balls in place.
Or you can just wrap some paper around the 8 mm part of the screw so it will be around 11.4-11.5 mm in total. Screw the nut on it, flip it and screw it back
You could, but there is risk involved there, that doesn’t exist to the same level as with the printed threaded model.
@Bud_Hammerton , @Igor_Kolesnik I’m sorry, but i dont understand why i have to flip the nuts.
It is usually flange down. To connect it to carriages it has to be flange up
@Bud_Hammerton you can use fancy tools if you have a printer to make them. This is my first so I was not able to do that. Had to improvise, not the first time))))
Ok. Good to know. Next time i will tell them to machine the right side of the ballscrew 
Well @Igor_Kolesnik , I totally understand, my first printer was and still is a Robo3D that I got cheap. Not the best, not the fastest, but helped me learn a lot about printing, Marlin and other things. So I have been building what I need to build the Spider. But I didn’t exactly start from scratch. I have some background in architecture and mechanical drawing, among other things. Built a lot of stuff out of wood, even built my own UAV. So that kinda helps. Sometimes I forget that some people interested in 3D printing really have very little background in manufacturing or in making stuff in general.
@Bud_Hammerton It is not that I don’t have any background. I worked two years for Materialize and have an engineering degree. My problems were that I did not have access to the printer and I really like McGyvering things as long as it is not affecting quality)))))
I use Golmart 1204 ball screws with Walters bed support. It works out great.
Thanks for all the replies drawing attention to my forgetfulness, I haven’t finished up my printing yet since I ran out of filament about 3/4 of the way through printing @Walter_Hsiao bed parts. I just got more yesterday, but since I am upgrading my source printer (from threaded rods to a real lead screws) I am holding off printing until it is completed. In the meanwhile I started extending the stepper wiring and putting on sheathing and connectors. Paracord makes a much more flexible wire sheathing material than TechFlex for small wires like stepper and limit switch wiring. All bigger bundles will be in TechFlex.