This holder will keep all your probes secured and out of the way.  

- 1 hole is 0.65", for temperature probe.

- 3 holes are 0.55" for other standard probes, such as pH, ORP, etc.

- Strong Neodymium magnets combined with a grippy oring hold the box securely in place on aquarium thicknesses up to 3/4"

- Magnets are completely encased in cell cast acrylic and will never get water in them.  No worries about rusting magnets causing water quality issues.

- Thumb screws on the front will lock probes in place.