Metric and inch-based threads are NEVER interchangeable. How are these two screw theads different? What`s TPI mean? What options are there to sort the 2 kinds of hardware out if mixed up? What do the numbers mean in thread specifications like M10x1.5 or UTS 3/8"-16NC? Watch and learn.
To count turns per whole inch or any whole number of mm`s you can line up your ruler to start at a root as well. Just make sure you count actual turns as a nut would travel.
Memorize terminology and reach proficiency with pitch calculations.