... ,Sub coupling,Full size, Slim hole and Over Size.Main Couplings listNameSizeGradeCharactersRemarksSucker Rod Coupling5 ... a layer of rust-proof, wear-proof and lessening friction alloy coating, based on the T ... 5140,covers Full sizes,Slim hole and Over size ,and has many types like Standard,Sub ... basic functions:wear proof,corrosion resisting and reducing the friction, and its lifetime is also longer,even ...