No. PT22430 this unit consists of a snug (No. PT18724) with two 4" long rods, one a 1/4" diameter, the other a 3/8" diameter. It is generally used with an indicator attached to No. PT22428 swivel post snug which slides onto the 1/4" diameter rod. The 3/8" rod will fit into the Nos. 252 and 657H gauge holders. It also has the ability to be held in chucks and adjusted to a wide range of heights and diameters.