Abstract: An apparatus for a drilling tool includes a pilot drilling bit, a reamer, and a pilot body which is disposed to support the reamer and the pilot drilling bit at the end of a casing tube. The reamer includes a closed position in which the parts of the tool are concentric with one another and displaceable through the casing tube, and an open position in which at least a part of the reamer is located radially outside the casing tube. The pilot body includes a male portion which extends through the reamer, the male portion of the pilot body forming a cam surface for transferring rotation energy to the reamer and for switching the reamer between the closed and open positions, and the male portion of the pilot body being insertable in a recess in the pilot drilling bit.