A turnbuckle is a threaded fastener used to tension (or ‘buckle’) components, such as suspension bridges and various metal structures.
There are two primary types of turnbuckles. One uses a screw and nut mechanism to expand the unit, the other uses a set screw and a cotter pin to contract the unit. A turnbuckle’s tension is usually measured by a torque wrench, but these aren’t always handy.
There are two ways of measuring a turnbuckle’s tension using a simpler tool:
1) Measure the resistance when you compress or twist it with your hand.
2) Use a string to measure when it spins freely or not.
Either way, you’ll have to know the length before tensioning.
Methodology To Measure A Turnbuckle:
There are several methods of measuring a turnbuckle’s length before torqueing, which includes using a tape measure and ruler, using flexible steel tape, using calipers, and using a pair of dividers.
- Measure the turnbuckle’s length, then mark a point mid-length and a point halfway between this point and one end.
- Grip the marked midpoint with a wrench or pliers and attempt to compress the unit. If it resists being compressed, it is longer than the pre-marked length. If it is easily compressed, it is shorter.
- For a turnbuckle that needs to be tightened with the cotter pin method instead of compression. Grip the marked midpoint with pliers and attempt to twist the unit. If it resists being twisted, it is longer than the pre-marked length. If it twists freely, it is shorter.
- For a turnbuckle that needs to be tightened with the screw and nut method instead of compression or twisting. Hold one end in your hand, then attempt to extend or contract the unit by rotating its other end. If it resists being extended or contracted, it is longer than the pre-marked length. If it easily extends or contracts, it is shorter.
- Mark the turnbuckle’s length with a pen or marker before removing your tools.
In practice, turnbuckles are usually available in standard lengths from the manufacturer. A look through a catalog will give an idea of what length you’re dealing with and thus how much tension it requires. This is usually given as a torque value which can be used to calculate the force on the structure this turnbuckle is holding up.
Frequently Asked Questions
The best way to tighten the cotter pin method turnbuckle is by using a torque wrench, though it can be done with another calibrated hand tool or even a hammer.
Alternatively, if you don’t have access to these tools, gripping the cotter pin with pliers and giving it a good whack is effective, although rougher, way to do it than preferred.
The best way to tighten a turnbuckle with the screw and nut method is by using a calibrated torque wrench, though it can be done with another tool.
A turnbuckle’s length is measured by either its stem (or the distance it has contracted) or the total length of all three wires inside. This can be done with a tape measure, flexible steel tape, calipers, or dividers. Once you know the diameter and length of your turnbuckle (and how much tension it needs to be applied with), you can determine the force it’s holding up. This is done using basic physics equations.