My point was that measuring a thread diameter with a ruler is simply not good enough to do a proper job. - Get it wrong & there are safety issues.
To avoid any possibility of measurement error, vernir or micrometer for the diameter & thread pitch gauges for the pitch is the minimum requirement. There are of course other measurement options. I'll not bother listing all the standard threads I know that are around 1/2" - never mind the ones invented by some folks when making something "fit".
Ian