A perfect tutorial on a simple task but one where we get many calls because customers overtighten then and split their mulitports. Hayward actually improved their heads a bit putting more material around the gauge threads, back in the old days i used to put a tee on the outlet (return) pipe and put a gauge there instead and just permanently seal the gauge hole. Oil filled pressure gauges are the way to go, sadly you'll never find them in a pool store here, only the cheapest offering are sold. I've gotten them from industrial suppliers for our uses. I once saw someone have a go at installing a gauge like this using a pipe wrench!