... coupling,class T coupling,Sub coupling,Full size, Slim hole and Over Size.Main Couplings listNameSizeGradeCharactersRemarksSucker Rod Coupling5/8”; 3/4 ... manufactured with a through hardness of between 16 and 23 Rc. This results in high tensile and fatigue strength for the sucker rod ... steel alloy AISI 5140,covers Full sizes,Slim hole and Over size ,and has many types like Standard,Sub OD ,with Big ...