Sucker Rod Pump
From Self-sufficiency
A steel rod that is used to make up the mechanical assembly between the surface and downhole components of a rod pumping system. Sucker rods are 25 to 30 ft [7 to 9 m] long and threaded at each end to enable the downhole components to be run and retrieved easily.
http://web.mit.edu/2.972/www/reports/sucker_rod_pump/sucker_rod_pump.html
