It doesn't seem to matter the brand or size... sharpening a chain and it seems like there is a pretty big variation of how hard the cutters and depth gauges are. Some insanely hard, brand new file skates across it. Others seemingly super soft. Even the stihl chains have noticeable variation. This must be intentional. The hardening process is very precise. Is it to allow some stretch to the chain, to have some links softer? Some other reason?