Identifying a piece of hardware holding a radio telescope dish

Hello,

My fellow students at RRCC have installed a donated radio telescope dish on campus. The dish has a rusted part that I'd like to learn more about so I can replace it. I don't know what it is called. The attached photo shows it circled in red. The part is meant to raise and lower the dish's azimuth by way of a turning a center piece that rotates around two threaded, large bolts on either end. I'd like ultimately to know how much it would have extended and how much it would have retracted if it were working. As it rests it is about 20 inches long. If I could figure out it max and min sizes it would help me select a new actuator to replace it. Does anyone know what it's called and how far these things can extend? (A ballpark answer like double or a third or that is the max or that is the min would help.)
Thanks
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It's a turnbuckle. You might be able to clean it up with WD40 and a brush.

When you replace it, consider coating it with silicon from a spray can (Marine store or auto). That will help it not oxidize.