Screws are cylindrical fasteners with raised external threads and a formed head. There is a slot in the head to hold a screwdriver bit for twisting the screw into another material. Screws, because of the thread, have greater strength of bonding than nails and, in most cases, are easily removed. The length of screws is measured in inches. The length of the screw needed should be based on having half the length extend into the material.
Sheet Metal Screws
Sheet metal screws are used to connect pieces of metal. They are also used for quick and strong fastening of metal to plastics, aluminum, hard rubber and plywood. These screws are characterized by having sharp threads that are good at bonding with other materials. The shaft is typically threaded all the way to the head. This allows for good retention to other materials.
Pan head screws come in either Phillips- or slotted-head varieties. These are distinctive in that the head is raised above the surface of the material being fastened. They are available in zinc-plated steel, and non-coated, white-coated and black-coated stainless steel.
Flat head screws, which come in Phillips- and slotted-head styles, are best countersunk into materials. These come in zinc-plated and stainless steel varieties.
Oval head screws resemble flat head screws, but have slightly more rounding on top to provide a more finished appearance. These screws, available in stainless steel and zinc-plated, come in Phillips and slotted heads.
Self-drilling screws come in pan head and flat head varieties. They are similar to the other screw types except for the addition of a drill point at the tip. These are fitted for only Phillips head screwdrivers and are made of zinc-plated and stainless steel.
Hex washer screws are sheet metal screws with a hexagonal head and washer attached to cap the shaft. These come in zinc-plated and stainless steel. They are also available in a standard self-drilling type as well as one with an additional bonded neoprene washer.
The use of steel and stainless steel for sheet metal screws is because they bond best with the metal while still forming a good bond with other materials. To avoid discoloration over time, screws are available with zinc plating to guard against this and rust. Stainless steel offers a high level of corrosion resistance and is preferred in high-moisture applications.
- "Sheet Metal Fabrication: Techniques and Tips for Beginners and Pros"; Eddie Paul; 2008
- "Ultimate Sheet Metal Fabrication Book"; Timothy Remus; 1999
- Photo Credit Image by Flickr.com, courtesy of Louise Docker
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