same warning from me about the detent spring. It's very easy to kink it with the plate on the telestock.
Best thing to do is back the castle nut all the way back then slide on the retainer plate then screw it into the receiver. When you get to the point where the buffer tube (receiver extention) is a couple of turns away from the hole, add the buffer retainer pin and spring holding it down will you screw the buffer tube in enough to hold the pin from flying out. They aren't like an A2 tube where you just screw them all the way in. You have to screw it in to the point of holding the pin in and allowing the key in the retainer plate to line up with the hole for it in the receiver. Next slip the detent spring in and slowly compress it with the retaining plate and hold it down tight while you tighten the castle nut by hand. At that point you'll want to use the tele stock wrench to tighten it the rest of the way.
That's about all there is to it.