... . Used to connect the sucker rod for the oil extraction 3. Basic Material: AISI 5140 Coat Layer: Ni60A Yantai Yunsheng ... , Class T couplings, Full size couplings and Slim Hole Couplings with the size range of 5/8", 3/4", 7/8", 1 ... 1) Material: AISI 5140 2) Standard: API Spec 11B 3) Size: 5/8",3/4", 7/8", 1", 1-1/8" 4) ... Smoothness: 3.1×10-3 5)Coat Thickness(in): 0.01in ~ 0.02in 6 ...