The following is excerpted from our reprint of “Woodworker’s Pocket Book,” edited by Charles H. Hayward. I have screwing on the brain (so to speak) because I’ve been teaching Kale about pilot holes and clearance holes. I could have just handed this book to Kale, and it likely would have provided more clarity than did I. And it is certainly more succinct!
– Fitz
Screws can be obtained in many metals and finishes, sizes and types.
METALS. The chief kinds are mild steel (iron) and brass, but in addition screws are made in copper, gunmetal, aluminium, and in a variety of finishes, such as Berlin blacked, galvanised, tinned, nickel-plated, electro-brassed, antique brassed, antique copper, electro-coppered, copper-oxydised, electro-silvered, and blued. The range of sizes is not so great in these fancy finishes.
TYPES. Countersunk head, raised head, and round head are the types mostly used. Size is taken from the position shown by arrows. Raised heads are frequently used with screw cups, which increase gripping area and give a neater appearance.
SIZES. Screws are classified by length and gauge. Illustration above shows from where length is taken. Gauge is the diameter of the shank and is the same in all lengths of screw. For instance, a 1-in. 9-gauge screw would have the same diameter and size of head as a 2-in. 9-gauge screw. Gauges range from 0000 to 50, but those from 4 up to 12 are most commonly used. Diagram shows five common gauges in actual size. [Ed note: The images here will resize to your device; they are not actual size] Order screws this way: ” 1 gross 1½-in. 9s, countersunk, iron.” It is always cheaper to buy by the gross than dozen.
SCREW HOLE SIZES. Two sizes of holes are needed when screwing – a thread hole and a shank hole. The former is the hole into which the screw bites its way, and should be smaller than the over-all diameter of the shank. The clearance hole should be a trifle fuller than the shank diameter. The table on the following page gives the various gauges of screws and the sizes required for the clearance and thread holes. A certain amount of latitude is possible. Softwoods will take smaller size of thread hole than hardwoods.
LUBRICATION. Lubricate screws before driving them in. It eases the work and prevents rusting. Vaseline is excellent. Be careful of mutton fat and Russian tallow, as the salt in them may cause corrosion.
FINDING THE GAUGE OF A SCREW. If you are uncertain of the gauge of a screw this simple method will give the exact answer in a few moments. Measure across the head of the screw, counting the measurement in sixteenths of an inch; double this number and subtract two. This is the gauge.
For example: a No. 10 screw (independent of length) will measure 3/8 in. or 6/16 in. This multiplied by two is 12/16 in.; less two is 10/16 in., or No. 10.
Take another case: the screw head measures 4-1/2 sixteenths; multiply by two=9; less two is 7, which is the screw gauge.
The table below gives the various gauges of screws and the sizes of the clearance and thread holes. It has been compiled from information supplied by Messrs. Nettlefold & Sons, Ltd.
When a long brass screw has to be driven into a hard wood it is advisable to drive in an iron screw of the same size first, as otherwise the resistance may cause the brass screw to snap off. Once the iron screw has been inserted it can be withdrawn and replaced by the brass screw.
The illustrations in this post, organized to be visually attractive, would make an excellent poster. Hint, hint. Hoping copyright would allow that, or that similar information and images from public domain books could be used. The table for pilot hole sizes would be particularly handy on the shop wall.
Thank you for explaining so much about screws! Like sun beams breaking through cloudcover after a rain, you make things clear.
I have noticed that steel screws and brass screws of the same size may differ in thread pitch so that last suggestion in the article might bear some modification.
Is there guidance on when to use different screw gauges? How about lengths based on the thickness of the boards being joined?
Thanks for publishing this. There’s always something to be learned in these posts.
Not in this book I’m afraid
Thank you, Megan!
I did not know how to determine screw gauge. I always thought, “Yah, no. 10 is bigger than no. 8,” but nothing more specific than that.
The “raised head” screws I see in stores are called “oval head”, which kinda makes sense as being between “flat head” and “round head”.
Also, when I read “screw cups”, my mind jumped to “finish washers”, but then I have seen something that is a “cup” that fits under a flat head (could also work with raised head) – that fills the countersink neatly. Exceedingly rare, but quite pretty. Finish washers sit proud of the material and provide a cup for the flat or oval head screw (oval, or raised, head being the preferred with a finish washer). Used a lot in the marine trades.
I wish there was such a thing as useful as an “enhanced drywall screw” (like the square drive screws from McFeeley’s and others), but pretty on top. There’s not.
I recently visited an art gallery/studio warehouse place in Cleveland – saw some interesting woodworking projects with VISIBLE construction-grade screws and knew two things – one is the artist is blind to beauty, and two is the pieces were not designed correctly, relying on screws for structure.
Love/Hate. Screws.
I remember using soap or wax for lubrication on screws. what do folks use today?
I use wax
Soap or wax.
Ancestor to the Infographic, which might be another product idea.
This post is such a shock. I needed this last week. I twisted off two screws working out the hole sizes for brass in cherry. Then I was told about the steel screw first trick. By the last screw I had it down, but it cost me a lot of time digging brass out of the backside of cherry.
I have the pocket book but I couldn’t find it at hand, so I ventured forth. Haste makes waste as always. The moral of the story: you can lead an idiot to knowledge, but you can’t make them think.
I have read much about fasteners and their history. Nowhere have I found an answer to this simple question: “Who devised the Type 17 screw point?” I think that there are Type A and Type B, but there is little information about them either. This may be one of life’s great mysteries.
With all respect to Mr. Hayward, he left out one of the more important types of screw: the bronze screw. Whether in flat head or raised (oval) head, the are much used in boats. They are not the same as brass screws by a long measure, being equally corrosion resistant (over centuries in salt water, for example) while at the same time being vastly stronger than brass in all measures and by some measures stronger than some stainless steel screws. When exposed, they offer a pleasant and sturdy appearance. More people should give them a try for outdoor projects.
A word of warning: I bought a box of #14 screws at the hardware store and discovered they had #14 heads and #10 bodies. Of course drywall, deck and construction screws are completely different than those described here.