Yeah, I found it wierd too when I started designing PCBs (as hobby) that “mill” actually stood for thousanth of an inch.
Probably for historical reasons, there are tons of things in the older domains within electronics that are based on inches rather than metric units: for example the spacing between the legs of a microchip in the older chip package formats (so called DIP, the ones with legs that go into holes) is exactly 0.1"
The sizes in more modern electronics isn’t usually based on inches anymore, but circuit boards are old tech (even if done with new materials) so there are still a number of measures in there which are based on inches.
Yeah, I found it wierd too when I started designing PCBs (as hobby) that “mill” actually stood for thousanth of an inch.
Probably for historical reasons, there are tons of things in the older domains within electronics that are based on inches rather than metric units: for example the spacing between the legs of a microchip in the older chip package formats (so called DIP, the ones with legs that go into holes) is exactly 0.1"
The sizes in more modern electronics isn’t usually based on inches anymore, but circuit boards are old tech (even if done with new materials) so there are still a number of measures in there which are based on inches.