Vermont Gage Steel No-Go Plug Gage, Tolerance Class X, 0.2500" Gage Diameter Supplied with a certificate of accuracy traceable to National Institute of Standards and Technology (NIST) No-go (-) gage for measuring the upper limit of a hole Available in a range of sizes in .0001 increments up to 1.0000 Made from tool steel 60/64 Rc cold stabilized for durability Class x (tolerance of .00004) for precision measurement