A new method for controlling the thrust vector of large solid propellant rocket motors has been developed. The key element of this approach to TVC is the Lockseal, a flexible joint that allows motion of the nozzle relative to the motor case. In comparison to the torques required for other types of solid motor movable nozzles, the torques required to flex the Lockseal joint are low and well defined.This paper describes the basic Lockseal from the user's standpoint. Included are details of construction, operating characteristics, and tradeoff considerations. A comparison between Lockseal and secondary injection TVC is included.