Why is it called a "countersink"?
December 12, 2022 3:36 PM   Subscribe

Countersinks are a conical flare-out at the top of a hole drilled for a screw. They're created so that the wood screws with the flared-out heads can sink far enough to make the tops of the screws flush with the surface of the wood. But why are they called that? A hole with a countersink doesn't counter sinking any more than a hole without one does. I have not seen any etymologies that explain this for me. Let me know if you have one!
posted by ignignokt to Writing & Language (12 answers total) 6 users marked this as a favorite
I don't know about the counter part of it, but it's not to prevent sinking, it's because it's already sunk. The hole is sunk into the material to be fastened, or it allows the head of the screw to be sunk down to the surface level of the fastened material. The counter makes sense to me in that way in as a regular kind of prefix for that kind of thing, but not in a way that I describe or think of other examples of at the moment.

And it's not just with the flared wood screws, it's a term that applies to any fastener hole that's depressed in that way.
posted by LionIndex at 3:49 PM on December 12, 2022

The countersink bit is the tool you use to drill pilot holes for countersunk screws, which means you want the screw head to be flush with the surface (or below it).

As in, sunk-into-the-counter, not sink-prevention. (Or maybe in the sense of the void being the inverse of the screw's shape). So what countersink bits do is standardize the pilot hole in that shape. The more basic way is to use a smaller bit for the length of the pilot hole and then enlarge the top.

(Here's more detail on the item itself, for anyone more familiar with word roots than fasteners.)
posted by snuffleupagus at 3:49 PM on December 12, 2022 [3 favorites]

Best answer: This English Language & Usage StackExchange post has some speculation and a quote from the OED suggesting that the “counter” part meant that the hole is a “counterpart” to the screw being sunk into the hole. But it doesn’t sound like the OED has a smoking gun explanation of where the word came from.

(Hopefully someone with access to the OED or another good etymology resource will come by with more info!)
posted by mskyle at 3:55 PM on December 12, 2022 [6 favorites]

Best answer: One of the meanings of the prefix "counter" is "complementary; corresponding".

You can see the countersink hole (or bit) as having a complementary or corresponding shape to the screw head that will fit into it, below the surface. As in "sunk" below the surface - this this "sink" part of "countersink".

This "counter" meaning "complementary shape" allowing the head of the screw or fastener to be "sunk" beneath the surface.
posted by flug at 3:57 PM on December 12, 2022 [18 favorites]

One of the meanings of the prefix "counter" is "complementary; corresponding".

That's it - an example I thought of is "counterflashing", is the complementary piece to your more standard flashing at a roof penetration or perimeter. It's not there to prevent the flashing from happening, it's there to allow it.
posted by LionIndex at 4:07 PM on December 12, 2022 [6 favorites]

Here's a temporary link to the OED but it isn't the huge entry I had hoped it would be.
posted by any portmanteau in a storm at 4:08 PM on December 12, 2022

Best answer: The OED entry that really enlivens this question is the one for the prefix counter-. It's one of these great early-alphabet OED entries that hasn't been overhauled since the entry was first published in 1893. For the first several letters of the alphabet, OED was still figuring out what its editorial voice was going to be, and so the etymology is a whole essay.

First, the ety for countersink, v. itself is just
Etymology: "counter- prefix, apparently in a sense akin to 8 b, the hole being the counterpart of that which is to be sunk in it"
The entry for counter doesn't actually have a sense numbered 8b, but we'll come back to that.

Then the ety for counter-, prefix includes this gem:
Counter has thus become a living element of the language, capable of entering into new combinations even with words of Germanic origin. It may be prefixed, when required, to almost any substantive expressing action, as motion , counter-motion , current , counter-current , or even to any word in which action or incidence is imputed, as measure , counter-measure , poison , counter-poison . Hence it is often viewed as an independent element, written separately, and practically treated as an adjective: see counter adj.
The sense that the countersink etymology referred to as "8 (b)" is now "g (b)" — I had to haul out my print OED to confirm this.

Moving away from etymologies and just into OED definitions, now: at the entry for counter-, sense 8(b) is:
Like Italian contra-, French contre-, often denoting that which is the counterpart of a thing or person, and hence the duplicate or parallel, the copy or substitute, or that which is the complementary, accessary, or subservient ‘second’ of another, = rear- comb. form, sub- prefix. counter-admiral n., counterdike n., counter-drain n., counter-walk n., counter-warden n. [compare contre-master n.]
So if the "sink" is the conical flare-out, the "counter" could indicate it as the "subservient second" of... the screw itself, to my mind.

But there's also something interesting at 8(a) that I think is worth mentioning:
Forming the opposite member or constituent of anything that has naturally two opposite parts, as counterbalance n., counterfoil n., counterpart n., counterpoise n., counterstock n., countertally n., etc.; or constituting a second thing of the same kind standing opposite, parallel to, or side by side with the original. counter-earth n.; often with notions of balancing, checking, sustaining thrust, or of mutual adaptation, correspondence, etc.; as in countercipher n., counter-copy n., counter-die n., countermark n., counter-seal n., countertype n.
I really appreciate the "mutual adaptation" idea here: the sink-flare is adapted to the conical flare of the screw, which itself has a flat/planar head to adapt it to the planar surface it is being sunk into.
posted by xueexueg at 5:40 PM on December 12, 2022 [24 favorites]

I've always assumed the "counter" is in the sense of "against". Now that I look, Chambers defines the "counter-" "combining form" as meaning "Signifying against". With "ORIGIN: Anglo-Fr countre, OFr contre, from L contrā against."

I never really thought through how that worked with sinking, but I guess like "sinking the hole against the wood" or "against - opposing - where the screw would normally be, above the wood".
posted by fabius at 5:09 AM on December 13, 2022

I do know it's not because of the angle of the countersink - the term counterbored is used when a similar thing is done, but where you are creating a large diameter section at the top of the hole to accommodate recessing a bolt that has a round head with parallel sides so the top of the bolt sits flush with whatever it's being recessed into.
posted by dg at 10:47 PM on December 13, 2022 [1 favorite]

The countersink bit is the tool you use to drill pilot holes for countersunk screws

You might have that the wrong way round. Countersink bits are quite bad at finding centre, so they're used after you drill the pilot
posted by scruss at 8:54 AM on December 18, 2022

^ this is more correct, technically and practically.
My use of woodworking terminology is as loose as my joinery.
posted by snuffleupagus at 9:52 PM on January 11

I use those bits with collars that go around a regular bit to drill the pilot and countersink at once.
posted by any portmanteau in a storm at 11:21 AM on January 12

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