These glycerin-filled gauges are a great addition to your pool equipment. Larger and easier to read than virtually all the standard gauges, they still fit 1/4" npt thread so it is as simple as unscrewing the old one, wrapping the new threads in 2-3 turns of teflon tape and screw it on. Hand tighten only. No tools required.
It is a good habit to check your filter PSI every time you walk past the pump and especially when you turn the pump on. Even a variation of 1/2 pound is easily detectable with these nice gauges.
Glycerin filled, they are freeze protected down to -4º F.