Neptune Systems designed the MPR - Magnetic Probe Rack specifically for the Apex. It will hold the larger diameter temperature probe, pH probe, ORP probe, and salinity probe.
Dimensions - 4" long by 2.5" deep with the screws all the way backed out.
Neptune has designed a Magnetic probe rack that will hold up to 4 probes with one hole being slightly over-sized to hold those larger probes like the Neptune temp probe. By simply placing the MPR in your sump or tank, you can now securely hold all your probes in a single spot. If a probe is left loose their is a good chance it may float with the business end being exposed to the air and causing a false reading. The Neptune MPR can work with glass up to 1/2" thick and keep all your probes secure and safe.