Sucker Rod Coupling The sucker rod couplings are used for connecting sucker rods, polished rods and sinker bars. ** The main types of sucker rod couplings are sucker rod couplings, polished rod couplings and sub-couplings. ** All of the three types have two classes: class T(through-hardened)and class SM (sprayed metal). **Material: carbon steel, alloy steel. **Specification:5/8", 3/4", 7/8"1", 1 1/8"
