... coupling,class T coupling,Sub coupling,Full size, Slim hole and Over Size.Main Couplings listNameSizeGradeCharactersRemarksSucker Rod Coupling5/8”; 3/ ... steel alloy AISI 5140,covers Full sizes,Slim hole and Over size ,and has many types like Standard,Sub OD ,with ... has three basic functions:wear proof,corrosion resisting and reducing the friction, and its lifetime is also longer,even twice of Class ...