How Do I Choose the Best Machine Screw?

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  • Written By: Alex Newth
  • Edited By: Angela B.
  • Last Modified Date: 14 January 2020
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A machine screw's strength means it often is used to join machine parts, and choosing the right screw involves many factors. The length and thickness of the machine screw is important, because the screw has to be long enough to join the pieces and thick enough to keep them together. This type of screw can be made from many different materials, including steel and nylon, and this also will determine the screw’s durability. There are many head shapes, such as Phillips head and slotted head, that will determine what type of drill or screwdriver can be used. There also are pan, hex and flat heads.

When choosing a machine screw, you should look at the pieces you have to join together. You should then choose a screw that is long enough to go through the pieces and thick enough to keep them together. Thickness can be determined by the material of the screw, the material of the pieces and how much stress the pieces will encounter during use. For length, the screw should be slightly longer than the conjoined pieces to ensure a nut can be placed on the other side of the screw to adhere them.


There are many materials used to make a machine screw. Most materials are made from metal, such as steel and brass, but nylon and plastic also are used. Each material will have a different strength, rust resistance, magnetism resistance and durability. You should choose a screw based on these properties and what your project specifically needs.

To fasten a machine screw, one uses a drill or screwdriver that has a certain head. The head on the screwdriver or drill must match the head on the screw, or the two will be incompatible. Choosing between the different screw heads normally comes down to the tool you have and whether you want a screw that has better torque — Phillips head — or more driving force — slotted head.

Along with the fitting at the top of the head, there are three different head types. A flat head is a completely flat top, and this normally is best for projects in which the screw should be flush against a surface. Pan heads stick up a bit and tend to be easier to remove, because they bump up slightly from the surface. Hex heads often can take more stress than the others, and they tend to be better for heavy-duty projects.


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