By Jim Speck – fastener expert, exclusively for Atlantic Fasteners
Are you often stumped as to how tight you should make critical socket head screws? If so, you’re not alone. Although the answer depends on numerous factors, we have a helpful tool that should make it easier.
First, some basics worth knowing:
Fasteners, like socket head screws, represent holding power. They work when you tighten them into place with a wrench or screw driver. That motion is called torque. Too little torque and your parts remain loose. Too much and the integrity of your assembly is compromised through over-loading and possible permanent warping.
Fasteners create clamping load, which is just enough tightness to keep parts from moving relative to one another. The trick is to create a target clamp load that matches the assembly requirements to the fastener’s potential. When tightened, threaded fasteners create clamp load by stretching and holding, like an extension spring. Below their maximum limit they stretch and try to spring back. Beyond their maximum limit, they stretch but can no longer spring back, remaining permanently deformed, which compromises their holding power.
Friction in the threads and under the head is an important factor in tightening fasteners like socket head screws. More than half of the work performed is to overcome friction. A smaller percentage is also consumed by torsion, which is the twisting of the threads. A screw or bolt pulled to its limit in straight tension is approximately 15% stronger than one torqued to its limit – the difference is twisting stress.
Now for some specifics on properly tightening socket head screws:
- Make sure you have the right size and strength socket head fastener for the application. This can’t be emphasized enough.
- Follow manufacturers’ tightening specifications, if they exist.
- If no specs exist, purchase this handy Holo-Krome, inch slide chart (metric is here) which gives you torque figures for socket set screws along with socket screws having flat, low, button, and socket cap heads. Make sure you read the footnote warnings as to adjusting values for different assembly types.
And as always, if you’re still uncertain, ask the folks at Atlantic Fasteners for help.