Abstract: This invention provides a substantially tubular sealing insert for use with a sucker rod for an oil well and a coupling adapted to engage the end of the sucker rod. The coupling has internal threads engaging external threads of the sucker rod, and the latter has an outward flange spaced from said external threads. The coupling has a part extending beyond the internal threads adapted to abut the flange and to define with the sucker rod an annular space located longitudinally between the threads and the flange, the annular space having a first section substantially parallel with the sucker rod axis and a second section extending radially outwardly adjacent the flange. The tubular sealing insert is of resilient material inert to the oil well environment, and is adapted for location in said annular space. The insert has at one end a flared portion adapted to be trapped in said second section of the annular space to seal the same.