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Stronger (and Prettier) Fastening in Wood with Countersunk Washers

Come for the functionality, stay for the visual pop

By Rain Noe - November 19, 2015

in Hand Tools | DIY

Fastening Wood with Screws 101: If you need to drive a flathead screw into a piece of wood quite close to an endgrain edge, and you just drive it in without pre-drilling and countersinking, you're gonna split it. And even if you do take the time to make a pilot hole, countersink it, and get the screw in without causing a split, there's no telling what will happen over time. As the wood moves or undergoes whatever stresses it encounters—let's say the two connected pieces of wood undergo shearing forces—the screw may begin to tilt, producing the split you worked to avoid.

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To solve this problem, Canadian woodworking supply company Lee Valley created these Countersunk Washers, which "prevent the normal tendency of screw heads to split stock. The washer/screw combination applies force the same way a pan-head screw does, but is counterbored to a flush position.

"These washers have a key role to play in renovations or external trim repair," they write, "since they allow you to pull warped trim into place with long screws and then finish over it."

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We stumbled across these Countersunk Washers in an eight-year-old article by Ed Sulis, a Nova Scotia man who wrote up his boat repair on the Popular Sailing blog. (You see what we go through to find youse some content?) While split boards were not a problem for Sulis, here's a photo and explanation from him on how these little gewgaws helped him out:

Many boats have Teak & Holly floorboards ( 5 mm teak and holly with 9 mm ply backing ) fastened to the boat structure with number 8 countersunk SS [stainless steel] screws. Over the years, the teak and holly top surface shows the dings and wear of age, plus the screw fasteners have enlarged the countersunk holes, and some fasteners have stripped the thread in the securing "fiberglass" structure underneath.

Photo by Ed Sulis

The floorboards in this photo are 25 years old, are from a CS 33 [a 33-foot sailboat manufactured by Canadian Sailcraft], and they show the effects of much use, but they remain structurally sound. No need to replace but a bit of surface sanding and a light coat of varnish on all surfaces and they remain very serviceable. To further improve the appearance, the ugly screw countersinks in the wood were lined with brass inserts (countersunk washers). The section of floorboard in the left of the photo has the countersink well worn and the floorboard in the right of the photo shows the up-grade method and parts.

They're certainly a damn sight better looking than the dark ring of a countersink you'd see around your average naked screw head. And though they were designed for a functional purpose, if you have a furniture piece you've designed with exposed screws, I can't help but think these would provide some nice visual pop, particularly if the screws and washers were in contrasting colors.

The countersinks are machined to accept an 82-degree screw head (standard for wood screws), and of course require some precision to bore the recess for them. Warns Sulis, "Care is needed here to centre the counterbores in the existing holes and to control the depth: a drill press is a must."

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They come in #6, #8 and #10 sizes, in either stainless steel or brass. A 10-pack will run you between $5.70 and $8.00 (USD, we think; you never can tell with those shifty Canadians). Check 'em out here.

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Dimitrios Grigoriou

9 years ago

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Having two different metals in intimate contact will increase the likelihood of oxidation, so contrasting colours should be combined with caution.

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- Pete Schupska
  
  Dimitrios Grigoriou
  
  9 years ago
  
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  2Z
  
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  Brass and Stainless Steel are generally OK together, except in the most extreme environments, and even then marginally OK. For indoor use, even in non-climate controlled spaces, there should be no problem.
  
  Generally speaking, for a salt-water environment keeping a difference of at least 0.15V on the Anodic Index is good practice to prevent galvanic corrosion. Brass is 0.4~0.45V and stainless 0.5~0.6V.
  
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Juan Cano

9 years ago

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Sent this link to a friend that works on old wooden boats, and he was like, "I gotta get some!"

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Peter Hendry

9 years ago

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I've got loads of these in a box in one of my boxes.
Had them for twenty odd years.
Now I know what they're for.
Cheers.

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Nick Stone

9 years ago

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These aren't knew - they've been around (in the uk at least) for at least 40 years to my knowledge. They do give a nice finish though...

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