... 40Cr) API SUB Sucker Rod Coupling,Class SM 1)Function:The sub sucker rod couplings are used ... 0.01in ~ 0.02in 6)Smoothness: 3.1×10-3 7)Basic Hardness: HRC 16-23 8)Surface Hardness ... 8"to3/4 ",3/4"to7/8". 7/8"to1", 1"to1-1/8" 12)Main specification of 3/4 ... sucker rod coupling Weight:0.92kg O.D.:1-13/16(46.04mm Length:4in(101.6mm) ... available in sizes of 5/8",3/4",7/8",1",1-1/8" If you are interested in any ...