... customer's request 3.Size: tubing coupling from 1.9" to 4-1/2",Casing coupling fro4-1/2"to 13-3 ... /8" 4.Type: NU, EU(tubing coupling), STC,LC,BTC(casing coupling). 5.Surface treatment: Whole phosphating, or inside ... joints, adapter pup-joints, adapter couplings, stabilizers, air-liquid separators, anchors of oil pumps and revolving sand gravitated device, etc. API 5CT tubing coupling