Diagram of the Space Shuttle Solid Rocket Booster field joint assembly. The top end of the lower rocket segment has a deep U-shaped cavity, or clevis, along its circumference. The bottom end of the top segment extends to form a tang that fits snugly into the clevis of the bottom segment. A series of holes through the outer branch of the clevis, through the tang and part way into the clevis inner branch, hold thick pins that lock the segments together. An outer band holds the pins in place. Two parallel grooves on the clevis inner branch hold O-rings that seal the gap between the tang and the clevis, keeping hot gases out.