This is the sensor installation kit. It even includes a cover plate in case you have to remove the sensor.

Using the Universal Retaining Ring the sensor is installed in any tank material of any thickness. The retaining ring is through-bolted the tank top with a special tool supplied by MMSI, called the Retaining Ring Spoon.

The spoon holds the nut, lock washer, flat washer under the tank surface while you screw the retaining screws from the top.

To cut a hole, a good quality hole cutter and a 3/8 variable speed hand drill is all you need. You wil cut a hole even in stainless steel remarkably quickly. The time to install a sensor is about 15 minutes.