The Moore & Wright Firm Joint Jenny Calipers are manufactured from polished tool steel and have a large headed nut and screw assembly that provides a firm and rigid friction joint, with no play. The leg which holds the round adjustable hardened point is offset and model 341 has a locating spur on the straight leg. The sizes listed are the effective leg length which is measured from the joint assembly. Note: firm joint caliper capacities are generally 1/3 greater than the effective leg length. Ref: UTTK3131