Assuming you are using a SIMILAR UNDER-SUIT as I did, i just used 2" 8/32 screws that went from the inside of the armor, through the plastic covers and through pre-drilled holes in the armor I made: View attachment 269686View attachment 269687View attachment 269683 Just finish them off with nuts and cut them. (the secret to cutting them is to mount the armor on fully, use the dremel to give them just a little notch, then undo the armor and finish the cut away from the plastic. That way the plastic won't melt from the heat)
For the torso, I use the screws to secure straps that buckle in around the sides. The straps are adjustable. View attachment 269684
And for the top, I have straps that can loosen quite a bit on the inside to allow my head to get through (you can't see it here but the inside is has an adjustable strap that can loosen on both sides.