Measure twice, cut once

Or in my case, measure at all, purchase once. I need a fitting to go on to our outside tap so that I can connect a hose to it. It "looks like" a three-quarter inch fitting. So I "borrow" a suitable fitting from Dad. Too big. So today I purchased a half inch fitting. Too small. If I’d bothered to measure it, I’d know that it is five-eights. Bah.