Okay, here is the easiest way I can think to explain this, if you have a saber ground blade (on the right) the top of the spine is not machined down so it will be the stock thickness with tolerance and if you add coating it will be thicker than .250 naturally. If you have a full height flat grind than the entire blade is machined and the top of the spine will be slightly thinner than the .250 stock thickness. If you look at a full height flat ground blade that is full exposed tang you will see a difference in the thickness from the tang to the blade where the blade is machined down.