Model JT921 replaces the JT920 with a more efficient engine and increased thrust and pullback power. A shorter version, JT921S, has a narrower pipe box and no fluid tank that allow it to handle work in tight spaces. JT921 does pilot bores up to 4 inches and backream diameters up to 8 inches. It has 9,000 pounds of thrust/pullback. A 50-hp Cat powers the unit, and the electrical system uses a busman system instead of a multiple-relay system.