3/8" x 18 National Pipe Taper Thread, 1-7/16" Across, Hexagon Die, Carbon Steel, Ideal For Plumbing, Air Applications & For Rethreading Where High Accuracy & Tolerance Thread Is Not Critical, Recommended For Use With Hexagon Die Stock, Die Can Be Used With A Wrench Or Socket When Space Is Limited, Designed For Hand Threading Work In A Variety Of Materials.