The Frame 5 Elevator Jackshaft tube is responsible for taking the push tube that comes directly from the control stick down the center of the Airframe and turns it into push pull cables that go down each side of the Airframe.
This view is looking aft. It demonstrates how the centre push rod is converted to the outer push/pull cables down the sides of the fuselage.
The LH side view with a surprising number of cables seen, shows the various holes they must pass through in the fuselage frames.
An overall view of the RH horn showing the holes in frame #5 that the control cables pass through. The set up cable just above the tube is for the rudder control.