... and SM, so do Ultra High Strength Sucker Rod Coupling, using 4142 steel barCOMPANY PROFILEYantai Yunsheng Petroleum Machine Accessories ... API 11B sucker rod couplings, including Spray Metal coupling, class T coupling, Sub OD coupling, with various spec. of Full size, ... RODS TOGETHER FOR DOWNHOLEOIL PUMPINGLIFE-SPANAt least 6 monthsBASIC HARDNESS HRC 16-23SURFACE HARDNESS AFTER SPRAY WELDINGHRC 56-62, ≥ ...