Just a little block to hold the magnet of a home alarm door sensor (reed switch). The magnet needed something to sit on in order to line up with the sensor.
The magnet is screwed on to the mount. Stuck sensor to the door and this mount to the door frame with foam tape.
Length of magnet in the photos is 55mm, distance between pilot holes is 38mm, elevation of magnet 22mm and width of base is 24mm.