Manufactured of a steel body and micro grain carbide tungsten sphere. The sphere is welded (not stuck) to the body and afterwards rectified; this allows the contact points to reach the best concentricity between the center of the sphere and the center of the body. Used together with inspection gages; diameter of the contact points depends on the connection to inspect. Their body comes with standard thread #4-48 UNF. Under request we can provide straight or thread M 2,5 shank.