... line with API SPEC 11B, with the size range of 5/8", 3/4", 7/8", 1", 1-1/8 ... ". 5/8 " FS API Class SM coupling1-Type: SM FS coupling2- ... Coupling diameter: 5/8 " -O.D: 1-1/2" [38.1mm] -I.D ... look forward to your early reply with much interest. PETROLEUM MACHINERY PART, API Class SM 5/8"FS couplings