The 120T-12/4473 requires that a 0.75" hole be drilled for the switch and a 0.37" hole for the magnet. The 0.75" switch mounting is desirable since extra wire and connections are more easily inserted into the larger hole for concealment. Also, should the need arise for testing or replacement, it would be easy to pull the switch, extend the extra wire and access the original connections. Installation is further enhanced by using a smaller 0.37" magnet to avoid the need to center a larger hold in a 1" to 1.5" thick door or window. This will allow you to offset the magnet should it be required. The 120T-12/4473 switch set was developed for and should only be used in openings with wood or aluminum frames.