0.2811"-0.4060" Tool Steel Class X Go(Plus Tolerance) 25 Piece Over/Under Gage Pin Set In Durable Plastic Case Vermont Gage Over/Under Sets Are Built Around One Nominal Diameter, Either Go(Plus) Or No-Go(Minus) Tolerance. Tweny-Four Additional Pins Are Supplied In .0001" Increments. Twelve Gages Above The Nominal Diameter And Twelve Gages Below. The Class X Tolerance Ensures A Separation Between Each Pin In The Range Around The Nominal Diameter. This Allows The Gage User To More Accurately Identify Where The Hole Is In Relation To The Nominal Hole Diameter. Nist Traceable. When Ordering, At Checkout, In The 'Additional Instructions' Field, Enter Your Nominal Gage Pin Size. Vermont Gage Usa Part #270104000