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Your tractor looks almost new. The link is like a turnbuckle. One set of right hand threads and one set of left hand threads.
The adjustment portion needs to be started on each set of threads at the same time so it takes up the slack evenly.
If someone has turned one end, then it may be bottomed out and although you can still see threads on the other end, you cannot use them.
If it is not easy to turn with the lock nut backed off something is wrong.
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Dave
M7040