There are many reasons why machine screws are in widespread use as a precision fastening as they come in a wide variety of fittings, including pan, pozidrive and slotted heads, with flush mounting or countersunk options being available.
Whilst typically they are made of stainless steel they also come in zinc plated and brass fittings. They come with coarse threads (24 threads per inch) and fine threads (32 threads per inch), and the grade of thread used will depend on their application.
Whilst they may look similar to self tapping screws, unlike self tappers they need a precise thread making in the steel (typically they are not used in wood) that they are going in to. They are also available in a wide range of diameters and lengths making them suitable for a very wide range of applications.
One other key difference between them and self tappers is that they have no point like a self tapping screw does and the end of them is machined flat instead, and as such they cannot be used to cut a thread in to any material, but will only screw in to a pre-threaded hole.
They have the additional advantage that they can either be screwed straight in to a threaded hole, or they can be used with a nut as a fastening. This adds to their versatility and means that they can be used to provide a very quick form of fastening. Indeed when used for fastening metal cases up they are often screwed in to caged nuts for speed of fastening.
Machine screws are used where a precise fitting is need and are often used when fitting machine parts or cases together. Typically a large number are made of stainless steel, as this is a really good benefit as they will not corrode allowing them to be unscrewed easily many years later when used in external applications.
They can vibrate loose if used in a harsh environment, however the fitting of nyloc nuts or the use of locking washers alleviates this problem. Nyloc nuts feature a nylon insert that forms a tight bond around the thread as the nut becomes tight, alleviating any vibration problems yet still allows the machine screw to be released very quickly.
Stainless steel screws are also inherently very strong and in the majority of instances the material they are screwed in to is likely to break before the screw does. These are just some of the many benefits of machine screws.
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