Don't leave your probes dangling in your sump or aquarium! With the AquaMaxx Magnetic Probe holder, you can get a more aesthetically pleasing and organized setup. No more pesky damages to your probes and no parameter swings because of air-exposed readings. The AquaMaxx Magnetic Probe holder holds up to four probes that accommodate two 1/2" (13mm) holes and two 11/16" (17mm) hole probes. The probe fits aquariums up to 1/2" thick. So if you're looking into an orderly and sleek fit, pick up yours today!