External Jaws: Large lower jaws that clamp around the outside of an object to measure thickness or outer diameter.Internal Jaws: Small upper jaws that expand inside an opening to measure internal slots or hole diameters.Depth Rod: A thin bar extending from the rear end used to gauge the depth of holes or steps.Locking Screw: A thumb screw located on the slider to clamp the jaws in place once a measurement is taken