These glycerin-filled psi 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 0.5 psi is easily detectable with these gauges. Freeze protected down to -4º F.