This product is produced by API standard and also ISO standard. The cylindrical surface and end face of the sucker rod coupling connections is a chamfering slant with an angle 14° <α< 30°. The junction of cylindrical surface and chamfering slant is a arc Chamfer less than < xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />1.67mm in radius, which all greatly avoid the scratches damage  and wear & corrosion  damage  on the pipeline wall during the touch between coupling cylindrical surface and the end face, so that the life of the coupling and pipeline are significantly Prolonged.