Understanding the Different Screw Threads

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close up photo of screw threads

Screw threads, also sometimes called helixes are ridges wrapped around a cone or cylinder. The threads can be on the outside like in a screw or bolt or inside like in a nut. Threads are essential in screws and help during fastening to assemble joints. They aid in temporary or permanent fastening. When used temporarily, the implication is that the assembly will be disassembled frequently without destroying the fastener.

They convey materials, transmit power, increase efficiency like in a car jack, or hold parts together. In other cases, threads control movement. In general, internal threads are made on the inner surfaces holed devices while external threads feature on the cover. The following are common thread profiles you will likely encounter:

The V thread

This thread has gained popularity globally so much so that there are ISO standards for it. Some countries used it as the metric thread for their applications. The V thread is sometimes called a unified thread. The slope of the threading features at 60 degrees. The profile shows up in standard proportions. The dimensions, however, will vary based on applications.

The square thread

screw thread mounted on a boardSquare threads are the most common. As the name suggests, they form a square. The sides of the flanks show up at 90 degrees to the thread’s axis. The thickness and the depth will be the size of half of the pitch. The crests and the root are square, with 90-degree corners and they work quickly. Sometimes the ridges are modified.

If you ask a screw supplier in Sydney, they will say that the most common use for this type of thread is in motion transmissions like in clamps and vices. It helps to convert fast rotary motion to a slower linear motion like in jacks and screw presses. There will be few threads in the square thread and low friction.

The acme thread

When a square thread is modified to become active at the base, it becomes an acme thread. The acme thread angles at 29 degrees. It has inclined sides that facilitate fast disengagement and engagement like in a lathe. The most common uses of this threading are in jack screws and break screws. This thread will help in transmitting power. Its shape will facilitate the engagement of split nuts.

The single and multi-threads

One can have many types of threading in one application as independent and separate entities. There are multi-start threads and single threads available in the market. Independent threads often go by the name starts. To have a full turn round for the bolt or screw, there has to be a movement in one thread. If the action is for more threads than one, that will be referred to as a multi-start thread. These threads are commonly used in applications where rapid motion is necessary.

Regardless of type, threads will lean to the left or right. Right-hand threads demand that the screw turns to the right to open. The opposite is true for left-hand threads. When getting screws, be sure to check the options that you get as trying to open the screw in the wrong direction can cause it to wear.


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