Okay, I have a dumb question. I'd like to use cable grips or glands to secure the power cord coming out of the controller box that I'm building. But I have no idea how they are sized. On Amazon, I see PG7, PG9, PG11, etc. But how do those sizes correspond to wire gauges? For example, I have a 10 gauge, 3 conductor stranded wire for my element, and a standard 4-conductor 10 gauge dryer cord for power. Can someone provide the Rosetta stone for deciphering this?