Haige provides full sizes and steel grades Tubing Couplings and Casing Couplings for oil and gas as per API Specification 5CT. Tubing Couplings Specifications: Diameters: 2 3/8", 2 7/8", 3 1/2", 4 1/2" Grades: J55, K55, N80-1, N80Q, L80, P110, Q125 Connections: EUE, NUE Other options: Special Beveled Couplings Special Clearance Couplings Directive 10 ( D-10 ) Couplings Special dimensions upon request Stocks availability: 2 3/8", 2 7/8", 3 1/2", 4 1/2"