The couplings produced by our company are good at stable quality which the technical parameters are completely complied with the requirements of API5CT and API5B latest standards. Meanwhile, the company has equipped with more than 30 sets CNC threading machines, is able to produce variety of steel grade couplings include STC, LTC, BTC and NU, EU threading couplings. Please visite our website: www.richsen.cn The size for Tubing couplings are ranged from 2-3/8'' to 4-1/2'', as well as 4-1/2'' to 20'' for Casing Couplings. The company can produce all kinds of couplings over 1 million pieces annually. If you have any questions, please contact Laura@richsen.cn in any time.