Abstract: A millout whipstock has a cylindrical body with a stabbing nose at the bottom and a deflection shoe at the top. A drill string extending through the deflection shoe is connected to a pressure housing keyed in a torque key housing in the body. A piston, mounted in a piston housing secured in the body beneath the pressure housing, has an upper portion extending through the pressure housing and is pinned in a raised position by shear pins. A slip expander at the bottom of the piston engages slips supported adjacent openings in the side wall of the body. A fluid path extending through the drill string, pressure housing, piston housing, and piston, is closed off by a rupture disk. The body is lowered by the drill string onto a cement plug in the casing. The slips are set by applying fluid pressure in the drill string to shear the shear pins and force the piston and expander downward wedging the slips outward to grip the casing.

Abstract: A two phase stepper motor having a rotor shaft with a multi-pole rotor and a stator assembly in magnetic flux relationship with the rotor. The stator assembly includes a plurality of sequentially stacked laminations which are each provided with eight stator poles with each immediately successive stator pole having an opposite phase and each being at a 45.degree. index spacing from the immediately adjacent lamination. The stepper motor also contains a multi-phase winding for energizing the stator poles to operate the rotor in successive discrete steps. The stepper motor housing includes first and second end pieces having a pair of triangular cross-section members forming notches therebetween on a first pair of oppositely disposed corners which receive and retain an abutment post on a second pair of oppositely disposed corners from the opposite end piece thereby interlocking the first and second end pieces relative to one another.