Tight enough that they don't fall out. But not so tight that they strip the threads
I'm not sure what torque rating they use but I'm sure someone here can chime in. B, C, D are pretty sturdy and you can really feel it when they are home and snug. A requires you to use something to stop the plate from turning, and has rubber inner to stop it backing out. Some would suggest a light lock tight as if any it going to break from over tightening this is it, and if any are really going to back out same again.
Be careful with nut "A". If you tighten it too much it will snap the threaded rod at the weld. Snug it up just enough. It is a nyloc nut and should not back out. I ordered extras and keep them on hand so I can use a new one each time.