fig1 and fig1 and described in detail later the end of the slip shaft 32 below the slip array 38 is threadedly connected to slip expansion mandrel 44 this threaded connection is afforded a fluid seal by 0 rings 58 and 60 ball bearings 44a are mounted in the tapered frusto conical surface 44b and in cooperation with ball bearings 44a serve to splay slip array 38 outward in response to downward movement of the slip piston 36 ball bearings 44a mounted on surface 44b create a convex surface on which slip segments 38b 38c 38d 38e and 38f of fig3 ride and provide hardened inserts eliminating the need to harden the upper surface 44b of the expansion mandrel 44 the slip expansion mandrel 44 is threadedly connected to the chemical module section 26 shown in fig1 0 rings not shown are employed to form a fluid seal for this connection the expansion mandrel 44 can be interchanged with a larger outside diameter expansion mandrel as will be detailed later the slip shaft 32 is provided with a longitudinal passage 32b and 32c which provides for fluid communication between the propellant section 24 and chemical section 26 the slip shaft 32 is also provided with one or more exhaust ports 32d which extend transversely from passage 32c to the exterior surface of slip shaft.