I have a small Makita I've mostly used with 4.5" cutoff discs. The disc is held by a kind of a washer under the disc & on the top side a threaded nut that uses their pin wrench to tighten. Today I installed a plastic body sanding disc. It is threaded for the shaft thread but you can't use either washer or nut which I found odd. Sorry didnt take a pic when installed. The direction it is threaded & motor direction means it is tightening, not loosening. But that was kind of the problem. It was a bugger to remove. It might be specific to my grinder but any input advice on this? Do they all only screw on like this?