(1) A bow spring or lever on a downhole tool which presses against the borehole wall to centralize the tool, to push the tool to the opposite side of the borehole, or to hold a sensor pad to the borehole wall.

(2) To prepare a perforating gun so that it will fire when the firing switch at the surface is operated. This usually requires connecting the detonator and/or completing the electrical wiring in the gun.