Octagonal Coupling Octagonal coupling fixes starter rod and transmitter housing and prevents overly tighten the threaded connection Part number FORWARD HDD rig Diameter 03-01-011-21-0712 RX11×44 72 mm 03-01-022-21-0712 RX22×80/RX33×120 92 mm 03-01-040-21-0712 RX40×160 125 mm