Joints created by Security nuts and Security bolts are all around us. They are in our cars, houses, furniture, and appliances. They are a vital component of most structures, vehicles, and industrial machines. Although we tend to take safety nut and safety bolts for granted, a bolted joint is a complex mechanism. When buying safety nuts and safety bolts, it is important to understand how they work and how to choose the right combination of parts for your application.
How Do Nuts and Bolts Work?
A typical bolt has two main components: a shaft and a head shaped to fit a tool like a wrench. Bolts have an externally threaded shaft. The shaft may be entirely threaded, or it may be divided into threaded and unthreaded portions. The unthreaded portion is often called the shank or the grip length. The most common bolt heads are hex-shaped. However, other variations exist for specialty applications.
A nut is a fastener with an internal thread and an external surface shaped to fit a tool. Like bolt heads, modern nuts are usually hex-shaped. Nuts are screwed onto bolts to form a bolted joint.
The purpose of a bolted joint is to prevent parts from moving relative to each other. Each bolt and nut component plays a role.
The bolt’s shaft prevents the parts from moving laterally (sideways) relative to each other.
The bolt’s head and the nut prevent parts from moving away from each other.
The clamping force generated by a correctly torqued nut and bolt joint prevents parts from moving radially (rotating relative to each other).
When installing a bolt with a nut, there are two main stages. In the first stage, the nut screws easily onto the bolt until the bolt head and the nut are in contact with the surface of the joined parts.
In the second stage, it becomes much harder to tighten the nut. That’s because further tightening—or torquing—elongates the bolt. Like an elastic band, this elongation generates tension in the bolt called the preload force. The preload force creates a clamping force that acts on the joined parts, holding them together.
When installing a nut and bolt, it’s essential to achieve the correct preload force. Or, to put it another way, you need to apply the proper amount of torque. Inadequate preload can cause parts to move relative to each other or the nut to unscrew from the bolt. Excessive preload can strip the bolt’s threads, causing the joint to fail.
look at the basic vocabulary used to describe threads.
Thread crest: the top of the helical ridge, the helix-shaped raised structure formed by the thread as it winds along the bolt’s shaft.
Thread root: the low point between two crests.
Thread flank: the side of the thread’s ridge between the root and the crest.
Thread angle: the angle of the V-shaped groove between two crests.
Helix angle: the angle of the thread relative to the axis of the shaft.
Thread pitch: the distance between corresponding points on adjacent thread surfaces measured in-line with the shaft of a bolt or the hole in a nut. You can also think of pitch as the distance between thread crests measured in a straight line along the bolt or nut.
Major diameter: the distance between crests on opposing sides of an externally threaded bolt’s shaft or between roots on an internally threaded nut.
Minor diameter: the distance between roots on opposing sides of an externally threaded shaft or crests on an internal thread.
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