The tool is used for cutting the inside PVC casing to install a pitless adapter that once had a well seal on the surface casing, then we fix them to how they are our installed today.
When you have a surface casing say 6" and the inside casing that is smaller around 4.5" or larger in our area and how we can tell when a new well driller comes along with 4" casing all the way to surface with no surface casing to install the pitless adapter says Merrill but the pump just barely goes by the pitless adapter (It still needs bigger casing if the person wants a sprinkler system later with a bigger pump, bigger drop pipe, and 1-1/4" pitless adapter or go back to a well seal). The inside casing is the casing that goes the rest of the way down to the bottom depth of the well. This inside casing comes up to high inside the surface casing (above frost line) where you have to cut the inside casing below the frost line to install a pitless adapter on the surface casing, so it doesn't hit the inside casing when putting it in place.