Types of screws and when to use them

We would be willing to bet that everyone reading this has a box or two – or maybe even an old tin can or pickle bottle – on a shelf in their garage, filled with an assortment of stainless steel screws of all shapes and sizes, as well as some made of other materials such as brass. Every time you need a screw, you go digging through those containers and just grab the ones that seem most suited. Screws are really the only type of fastener that you can take this multi-purpose approach with. You can use a sheet metal screw on wood if you have to, for example, even though it’s not the best for the situation. 

The conventional wisdom remains the same for all repair and building work: it’s always best to have the right tools for the job. Screws are designed with certain materials and functions in mind and you will get the most out of them if you use them to do what they were made for. To help you with these, we have drawn up a list of the three basic types of screw, describing each of them and their primary purposes.

Wood screws

Screws designed for use on wood have wide and coarse threads – especially at the end of the screw – and the top part of the shank often has no thread at all. These screws are designed to move smoothly through the wood, essentially cutting through the fibers, reducing resistance and splintering. They often have flat heads as most carpentry jobs require the heads to be flush with the wood – but not always. There are also ones with visible round heads or oval heads. A good rule of thumb for selecting the right length of screw is to remember that about 1-1½ times the length of the screw should go into the adjoining board. You can test this by holding the screw against the workpiece and making a rough measurement.

Drywall screws

There are two subtypes here: S-type, which is used to attach drywall to metal studs and W-type, which is for attaching drywall to wood. S-types have a finer thread and a self-tapping tip. W-types, on the other hand, have coarser threads and require more drilling.

Sheet metal screws

These come in a bewildering array of sizes and types, and are the most multipurpose variety of screw, used to join anything from plastics, rubber and even plywood to – well, sheet metal! The most common types are A, B and AB. They tend to have a finer, sharper and tighter thread than wood screws and can have flat, oval or hex washer heads.

Self-tapping

All of the above types can come in self-tapping forms. These cut out the need to drill as they cut their own holes as they are inserted.

Other factors to consider are the materials out of which the screws are made. There are various types of stainless steel, for example and each different alloy will be more suitable for different types of screw. Screws made out of a molybdenum-enriched type of stainless steel are intended for marine uses, for example. Speak to the Marsh Fasteners about the different types of steel used in screws and which are best suited for your projects. 

There you have it. Hopefully this will help you understand the differences between stainless steel screw types and help you to finish that next job properly. For more information, contact Marsh Fasteners, take a look at more articles in this blog, or visit our product pages.

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