Blog: Screw It! By: John Heisz
I have driven a lot of screws. Screws of nearly every possible variety, quality, length and size. Self drilling, self tapping (they are different), wood, metal, concrete, you name it. I’m not boasting (sorry stuff to brag about anyway), just stating the facts. In short, I know a few things about screws.
First thing I know is that they are not created equal. Screws are manufactured, and are victim to the same variability as other manufactured products: some are better than others. An excellent example are the typical screws that come with cheap window blinds, and how they are so soft they strip out or twist off as soon as they encounter any resistance. Another example are the screws that are found in those 10 piece blister packs at a discount store.
Unfortunately, there isn’t any reliable way to tell if a screw is good quality without buying it and trying it out. Taking it for granted that a large retail hardware store
will have good quality fasteners can be a mistake.
I’ll cite a local example (by local, I mean Canadian): there is a large national chain of stores that, for the most part, sells screws of very low quality. I’ll assume this is in an attempt to keep cost down to compete with other, similar stores. The fact is, 999 out of 1000 consumers are completely ignorant of this and probably don’t care, and this was most likely a major reason why the purchasing department settled for the lower quality. If you only lose 1 customer out of 1000 on something like screws, you still come out on top. Of course, this strategy has been applied to other store items as well, not just screws.
Aside from the differences in quality, there are differences in type and what they are best suited for. Sheet metal screws are designed to fasten 2 (or more) layers of sheet metal (steel, usually) tightly together. They can be used for other purposes – the design feature that makes them sheet metal screws doesn’t hinder their performance for other tasks. They are threaded all the way up their length and are hard and tough. In metal, they require a pilot hole of the correct size prior to driving.
Self drilling metal screws pre-drill a pilot hole before the screw enters. These are excellent for thinner metal, as long as the drill point is long enough to make it through before the threads engage. They will work in wood, but there really should be a pilot hole drilled for them. Even with a hole, the over-all thread depth is only a portion of the screw length, so there will be less holding power. These screws are hard and tough, although the extra hardening to create the drill point can make them brittle enough to break if stressed.
Wood screws are designed for fastening wood and other materials to wood. They are generally tough and hard to break and are typically only threaded on the first 2/3 of their length, to allow the outermost part that is being fastened to pull down tight against the part underneath. These will work with or without pilot holes, but for harder material and to avoid splitting, pilot holes should be drilled. I have found a wide range in quality for wood screws, from outstanding to unacceptable. Unacceptable (for me) is a screw that cannot be driven into hardwood without breaking or stripping out. Truly good quality wood screws should easily drive fully into hard maple without the need to drill a pilot hole.
Drywall screws were originally designed to fasten wallboard to metal studs. The screws are hardened, to allow them to pierce the metal without drilling a pilot hole, and this hardening leaves the screws very brittle and easily broken.
There are 2 varieties: fine thread, for metal studs, and course thread, for wood studs. In spite of their use for wood stud framing, the course thread version is manufactured in exactly the same way as the fine thread type: it is just as hard and brittle. These are excellent for screwing on drywall, but come up short for nearly every other application, woodworking included. This is demonstrated in this video:
Some humour, but the point is valid: the screws snap off quite easily and consistently. For those of you that have assembled anything with these screws and had the head break off, you know exactly what I mean. For me, the likelyhood that this will happen outweighs the extra effort and cost of finding good quality screws.