This is a probe holder that will hold the majority of PH and ORP probes. American Marine, Pinpoint etc. You can use it to install a probe into a reactor (i.e. Calicium) or sump.

Simply drill a hole, install the bulkhead, and then insert the probe and tighten the holder down around the probe.

This bulkhead does not have a gasket, so would not be water tight after installed unless sealed.