Haige provides full sizes and steel grades API 5CT Casing Couplings and API5CT Tubing Couplings for oil and gas field. API 5CT Casing Couplings Specifications: Diameters: 4 1/2" through 20" Grades: J55, K55, N80-1, N80Q, L80, P110, Q125 Connections: STC, LTC, BTC Other options: Special Clearance Couplings Special Beveled Coupling Directive 10 ( D-10 ) Couplings Special dimensions upon request Stocks availability: 4 1/2", 5 1/2", 7", 9 5/8", 13 3/8", 20"