Personally, I wouldn't be throwing away a blade plate unless when you remove the blades, you can see that the metal around the holes has been worn down rather substantially. I suggest you clean it up so you can see what condition it is in, and if it is OK, look at the parts to see why the nut will not screw down the thread slightly further. If the blade plate is OK and you have run out of thread, my solution would be to fit a washer of suitable thickness to the opposite side of the blade plate to the side the blade goes on. If you need to do that, though, be careful to fit identical washers to each blade, or you will put the rotating system out of balance, which is a bad idea.
