3-1/2-8 ANPT (Aeronautical National Pipe Taper (thread gauge)) BASIC L-1 RING GAGE Class X NIST traceable Tool steel RC 60/62 (cold stabilized) shipped in polly bag certificate of accuracy with each ring (these gages are manufactured to order delivery is 6 weeks aprox). Certificate of Accuracy is included.Click HERE to read about additional Long Form Cert.