Lag screws or lag bolts are known for toughness and reliability. They are sturdy, which makes them ideal to connect heavy materials. Also known as hex head lag screws, these units are made of different types of materials. An aluminum screw is lighter than a steel screw (iron alloy and carbon), but is less resistant since steel has better metallurgical capacity than aluminum.
A duralumin alloy boosts the strength capabilities of aluminum but decreases the toughness. Harder metals are less tenacious. Most special alloys of steels, bronzes and stainless steels contain a variable proportion of metals to adapt their use to a specific application.
It is important to use the right screw for each application. If a screw with too much strength (hardness) is not adjusted to the design value, it could break because it is too hard. This is because high tension screws have lower fatigue strength than screws with a lower tension value. A screw composed of a softer alloy could be deformed, but without breaking.
This eliminates the need to remove it, but it can continue fulfilling its role. The ISO standard is marked with two numbers on the head of the screw, for example “8.8”. The first number indicates the tensile strength (the hardness of the material); the second number refers to the resistance to yield point, that is, the tenacity of the material.
If a screw is marked as 8.8, it has a hardness (tensile strength) of 800 MPa (megapascals) and a tenacity (tensile strength) of 80 percent. A mark of 10.9 indicates a tension value of 1000 MPa with a resistance to yield point of 900 MPa — 90 percent of tensile strength.
The screws can support a greater weight or traction, but exceeding their capacity will cause a crack. Buy wholesale lag screws in California made with harder alloys can withstand greater weight or traction, but they also have a limit and less tenacity than bolts made in softer alloys. If you use a screw that has been tightly adjusted, whatever its hardness, it can break easily because its tensile strength (tenacity) is very low.
Most screws have a right-hand thread. For special applications, such as machine shafts and lock nuts, they have a left-hand thread. The screws on the wheels of industrial vehicles have threads with a different direction to the right than those fitted to the left.
In this way the screws tend to tighten when the wheels turn in the direction of travel. Also, the combination of right and left threads is used in threaded tensioners. The type of thread, metric or Whitworth has different physical characteristics.
