A turnbuckle is a mechanical screw device consisting of two threaded terminals and a threaded barrel. Figure 2-35 shows a typical turnbuckle assembly. Turnbuckles are fitted in the cable assembly for the purpose of making minor adjustments in cable length and for adjusting cable tension. One of the terminals has right-hand threads

Figure 2-34.-Thimble, bashing, and shackle fittings.

Figure 2-35.Typical turnbuckle assembly.

and the other has left-hand threads, The barrel has matching right- and left-hand threads internally. The end of the barrel, with left-hand threads inside, can usually be identified by either a groove or knurl around the end of the barrel. Barrels and terminals are available in both long and short lengths. When you install a turnbuckle in a control system, it is necessary to screw both of the terminals an equal number of turns into the turnbuckle barrel. It is also essential that all turnbuckle terminals be screwed into the barrel at least until not more than three threads are exposed. On initial installation, the turnbuckle terminals should not be screwed inside the turnbuckle barrel more than four threads. Figure 2-36 shows turnbuckle thread tolerances. 

After a turnbuckle is properly adjusted, it must be safetied. There are several methods of safetying turnbuckles. However, only two methods have been adopted as standard procedures by the services. These methods are discussed later in this chapter.