How to tell screws apart

Which screws are for what? Here's how to organize your pile

By Allan BritnellAllan Britnell

115_istock_screws

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So this is the weekend you’re finally going to tackle the cottage “to do” list. Job one: Wade through that giant coffee can full of screws to see if you have the fasteners you need for the tasks at hand. The simplest way to tell them apart is by colour.

1. The black ones are drywall screws, cheap and useful for many odd jobs, but not very strong. The tint comes from a phosphate coating that prevents wet drywall compound from corroding the screw head.

2. Blue ones are masonry screws, used for fastening things to brick, mortar, block, or rock, though you have to drill a pilot hole first.

3. Golden-hued screws are brass or, more likely, brass-plated. The brass won’t rust, which makes these screws an ­attractive choice for boat fittings, but they are significantly weaker than equally rustproof stainless steel.

4. Brown or green ones are corrosion-resistant deck screws. But unless you bought them in the last year or so you’ll need new ones. ­Pressure-treated (PT) lumber manufacturers recently changed the chemicals they use to a formulation that’s extremely corrosive to the wrong hardware. If you’re building with the new PT wood, buy fasteners labelled “ACQ compatible.”

5. The bulk of your pile are probably shiny silver screws. The short, sharp-tipped ones with round heads and threads spiralling up the entire shaft are sheet metal screws (a.k.a. self-tapping screws) that can bite into thin metal, such as aluminum eavestroughing.

6. Any with blunt tips are machine screws, essentially threaded bolts that are tightened with a screwdriver. They’re commonly used in electrical work and to affix cabinet handles.

7. Most of the remaining ones are wood screws, with coarse threads and a smooth section at the top of the shaft. Some are made of corrosion-resistant stainless steel, and others of cheaper, everyday steel. You can’t tell them apart by sight but, luckily, there’s a simple trick to sorting them out. Grab a magnet and run it through the pile; any that cling to the magnet are ordinary steel, the remaining ones are almost certainly stainless.

This article was originally published on December 20, 2010


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