Abstract: A down hole drilling tool activating mechanism is provided which will adjustably activate tool elements such as stabilizer pads by a mandrel which will move vertically against a bias spring and has inclined surfaces to bear on the inside of the adjustable pads creating variable diameters. The mandrel has a series of flexible fingers which engage the main body of the tool. A male spline element is provided which moves vertically within the body of the tool so that a portion thereof moves between a position in which it engages the fingers and forces them into engagement thereby locking the mandrel against vertical movement and a second unlocked position in which the portion is removed from the fingers allowing them to flex and allowing them to disengage the body so that the mandrel may move vertically changing the adjustment of the tool.