Manufactured from polished tool steel with 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 TA179A 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.