Designed for US 1803 & 1814 Harpers Ferry barrels. 24 inch long rib is taller than normal and fits the round portion of the barrel. These ribs develop a curve due to the stress being released from the metal during machining. This curve in no way makes the rib unserviceable. In fact, it aids in soldering the rib to the barrel, but you may straighten them by hand if desired.
