The Clevis Rod and the Turnbuckle Rod offer the ability to provide tensile strength by increasing their tension as they are tightened. The tightening is done by opposing left hand and right hand threads. In the Clevis Rod drawing shown below rotating the threaded rod overhand towards the installer it will draw the two Clevises closer, creating more tension. Rotate the Rod overhand away from the installer will move the clevises away from each other, relieving tension.
The Turnbuckle Rod works with the same premise but the Rods do not rotate. The center Turnbuckle does. A Turnbuckle will always be threaded left hand / right hand. Rotating the Turnbuckle draws the two rods closer together or farther apart.
Following this logic a Clevis Rod should have one Clevis threaded left hand. A turnbuckle rod should have both Clevises threaded right hand. We sometimes see Turnbuckle Rod drawings with one Clevis threaded left hand. While it will function just as well as the one shown above, the left hand threads serve no purpose. The tensioning is done by the Turnbuckle. In cases like this using a left threaded Clevis will only serve to confuse the erectors and delay installation.
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