Gauge material and heat treatment plays a very important role in obtaining a dimensionally stable and long life gauge. We use an OHNS Tungsten quality oil hardened non shrinking steel or a 20MnCr5 steel (for small thread rings). The gauge material is duly carburized hardened and tempered. A cryogenic treatment is carried out to increase the performance of the material. This cryogenic treatment is not a substitute for heat treatment, but rather an extension of the heating, quenching and tempering cycle. The process involves a slow controlled cooling, holding at cryogenic temperature for a specific hold time and then allowing to return to room temperature slowly. This process transforms all retained austenite to martensite. The end result is a very stable material which is 100% martensite and very hard RC 58-62. Without cryogenic treatment these steels may contain significant amounts of retained austenite which is a weak, soft, easily abraded micro constituent of steel.
All API 5B/7-2 are precision ground on CNC grinding machines. These Grinding machines are state of the art in grinding technology.
When necessary hand lapping is the finishing process that removes small amounts of material from the gauge surface to bring it within its final tolerance limits. It is the final procedure when machines cannot do the job, and of paramount importance. This process of feeling a millionth's of inch is a true art.
All our gauges go through final inspection in a temperature controlled (20 degrees +/- .5 degree C) metrology lab. All API Master gauges are fully traceable to either NIST or NIM . Our long form certificate of inspection provides as much detail as possible showing evidence of dimensional compliance. We understand quality system documentation as well as value associated with it; and as a result we provide long form certificates FREE with every gauge we sell regardless of price.
If the threaded components like nuts and bolts have to be coated then it is necessary to check them prior to coating. The gauge can be suitably designed to check the before coating size depending upon the coating thickness. Normally it is only the go limit gauge which is necessary to be used for checking before coating. The component near to nogo limit automatically falls within the tolerance limit after coating.
Normally coating thickness 0.001″. Here the thickness is considered as either an increase or decrease in the pitch diameter. If the coating thickness considered normal to the thread flanks, the variation in diameter is four times the thickness for threads with 60 degree angle and slightly less for 55 degree.