... of Full size,Slim Hole, Over Size, with Big Chamfer ,with Wrench Flat,with Bidirectional Cambered Surface Protection .And the thread size ... T sucker rod couplings are manufactured with a through hardness of between 16and 23 Rc. This results in high tensile ... and has many types like Standard,Sub OD ,with Big Chamfer ,with Wrench Flat,with Bidirectional Cambered surface protection. It has three basic ...