Enter the distance from the shell cylinder to the beginning of the knuckle for an expansion joint with an inside knuckle. Enter the distance from the outer cylinder to the intersection of the expansion joint web and the outer diameter for joints with a square outside corner. In both cases this distance is frequently zero and, for an expansion joint with an outside radius but no outside cylinder, this distance is the distance from the end of the knuckle to the symmetrical centerline of the joint.