Abstract: Apparatus which is well suited for positioning a pin to immobilize a circuit breaker switch comprises an elongated base member and an aperture-defining means, such as a wire or plate, fastened to the base member. The base member is elongated and has a longitudinal axis, an upper face, and a transverse groove extending across the upper face. The defining means is positioned across the transverse groove and in a plane parallel to the longitudinal axis of the base member. A portion of the aperture defined by the aperture-defining means is positioned in alignment with the transverse groove. A pin having longitudinal axis, a preferably generally rectangular or square cross section, and a plurality of longitudinally spaced apart grooves is positioned in the groove of the base member and through a portion of the aperture to immobilize a breaker switch positioned alongside the elongated base member. A lock is also passed through the aperture to block extrication of the pin.