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How to Decode Screws

Ask This Old House general contractor Tom Silva explains the uses and purposes of different types of screws

1. Tom shared a few different tips about screws and which ones he uses for what projects. Here are a few of his tips below:
a. Wood screws have a coarse thread for driving into material. They shouldn’t be confused with bolts, which have machine threads and require a nut to secure them.
b. Drywall screws should be used for drywall. They aren’t strong enough to handle other types of connections.
c. Screw heads come in a few different varieties. Flathead and Phillips head are common screws, but Tom prefers to use a star or torx head screw because they’re less likely to strip.
d. Check each screw to determine if it’s rated for indoor or outdoor use.
e. To determine the appropriate size screw to use for a project, take the thickness of the material being attached and pick a screw that’s roughly 2.5x that.
2. Screws all come with a labeling system. Here’s how it works:
a. The diameter is indicated by a # sign. That’s how thick the screw is. The higher the number, the thicker the screw.
b. The height of the screw is labeled in inches and usually is marked right next to the diameter.
3. They sell kits (and they’re also usually on display at hardware stores and home centers) that allow you to drop the screw into a hole to determine what it is.

All the different screws Tom demonstrated can be found at home centers. The gauge Tom demonstrated to help determine the correct screw head size is called a bolt gauge and can be found at home centers as well.