The common oilfield API-5CT casing couplings include J55, K55, N80 and P110 in accordance with API 5CT/5B, can be classified as STC (short thread), LTC (long thread) BTC (buttress thread) and premium connections. We cover a size from 4-1/2″ to 20″,STC, LTC and BTC, we also manufacture premium connections based on our customer enquiry.