For use with V-anvil and conical spindle inserts for measuring pitch diameters of screw threads (sold separately) Vernier scale in metric units with slanted barrel markings to help reduce parallax errors for taking precise outside diameter (OD) measurements Knurled friction drive thimble mechanism helps provide uniform pressure for precise, repeatable measurement Hammertone, baked enamel finish for protection and durability of frame Tungsten carbide facing on spindle and anvil provides wear resistance