GMCO Grade C and D Rotary Drilling Couplings have set the industry standard for over a decade and are were the first swaged-on grade D fitting to be successfully marked in the world. They are a one piece welded design and provide a permanent end connection to high pressure API grade C and D drilling hoses for use in the toughest oil field applications. Constructed of coupling grade schedule 160 N/L 80 4130 and special George Myer spec A 513 DOM tubing materials to provide years of trouble free service. GMCO Grade D Swage Fittings are specially designed for use with a wide verity of manufactures’ steel cable reinforced drilling hoses and require no set screws for coupling retention.