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(Non-english questioner) To countersink means to drill a sloped hole so that screw heads can sink into the material to be hidden.

In German for example the term for this action is "senken", which would translate to only "sink" (not "countersink", which would literally translate to German "gegensenken" - which doesn't make any sense in German).

I know the followng meanings of "counter":

  • a "mechanism" to increase numbers
  • something like "opposite" or "reverse" (like in "counterattack")
  • the furniture in a shop or bar where the salesperson works

None of them makes sense for screws. What exactly does "counter" mean here?

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    Since the pocket for the screwhead is secondary to the hole the screw drives into, that may make the counter part. When you counter an offer, you make a secondary offer. Commented Oct 28, 2020 at 20:07
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    Makes sense to me. You "counter" the conical shape of the bottom of a flat-head screw. Commented Oct 28, 2020 at 20:08
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    "Countersink" can also refer to a cylindrical depression to accommodate a cylindrical screw head (such as a socket-head cap screw) so the top sits below flush with the surface. Commented Oct 29, 2020 at 4:51
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    Cylibrical depressions are called counterbores, not countersinks. Commented Oct 29, 2020 at 10:35
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    @FooBar The secondary tool- whether it's a countersink or a counterbore- is applied against the hole made by (or centre point used by) the primary tool. I suggest that it's bad Latin: abuse of "contra" (against) when "supra" (above) might have been more appropriate... draughtsmen and fitters are renowned for that sort of thing. Commented Oct 29, 2020 at 14:05

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The conjecture on this in the OED says

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.

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  • Thanks. So the screw is sunk into the countersink. People always say "countersinking the screw", which would be wrong I believe. They countersink (the hole) first and simply sink the screw into it afterwards. Commented Oct 28, 2020 at 20:23
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    Screws with conical heads designed for these holes are called "countersunk screws" in the fastener trade. Commented Oct 28, 2020 at 20:28
  • However, cylinder head screws are never called 'counterbore'. That's why I really doubt that the prefix 'counter' in 'countersink' and 'counterbore' refers to the relation between hole and screw, but actually indicates the relation between primary (usually cylindrical) hole and secondary bore or cone. The secondary bore or cone simply counters the primar hole. I'll make this an answer. Commented Jul 20 at 19:35
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My grandfather was a blacksmith (now long dead). My understanding is that a countersink (also called a bob-punch), is used to form a depression in the surface of plates to be joined together when rivetting. Without this, the head of the rivet projects entirely and is subject to damage. If the head is broken off, the rivet will sink into the plate. The indentation counters any tendency to sink. I suspect the term also applies to indentations for horseshoe nails.

Unfortunately my grandfather and my father are deceased and I can't find anything online to support what I'm saying.

I'll leave this here for now and see if I can find anything further.

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    The term also applies to wood screws with conical heads that go in flush with the wood surface. I don't dispute the blacksmithing meaning you present, but be aware that it's not restricted to blacksmithing. IDK which meaning came first. Commented Oct 29, 2020 at 4:30
  • And yet, it seems to be the same meaning. If you used a screw with a round head, it would protrude out of the wood and risk being sheared off, in which case, the body of the screw would sink further into the wood. Commented Oct 29, 2020 at 9:05
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Google's Ngram viewer returns results for 'countersink' that indicate that it was a new word in the early 19thC. It does not appear in the corpus at all before 1820 and did not take off until about 1860. This indicates that "countersinking" was a process associated with industrialisation.

The Lexico entry for counter gives an uncommon definition which seems to be relevant.

The back part of a shoe or boot, enclosing the heel.

For which it gives the origin as

Mid 19th century abbreviation of counterfort ‘buttress’, from French contrefort.

The mid 19thC origin of the shoemaking term matches quite well with the appearance of "countersink" in the literature and "countersinking" a hole so that the head of a screw or other fastener fits below the surface certainly improves the strength of the join and could be said to "buttress" the fastener. I suspect that "countersink" also derives, perhaps in part, from counterfort.

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The etymology seems very murky, but my way to remember the meaning and difference between countersink and counterbore is thus: if you are building a countertop (furniture), then you don't want screw/bolt heads protruding. So you bore a little extra for the screw/bolt head, hence 'counter-bore.' Then if you slope the walls of your extra boring, it resembles a drain aka sink, hence 'counter-sink.' I know that this doesn't line up with the past-tense 'counter-sunk,' but the noun "the sink in your kitchen" and the verb "to sink into quicksand" are obviously common in origin.

From the other couple of languages I've studied, it seems that because english lacks a lot of explicit grammatical features of other indo-european languages and instead relies more on context of usage, the process of noun-ifying verbs and verb-ifying nouns can have ambiguous results.

All in all I think it's simply too murky of a history to try to pluck a thread of causality from unless you're a scholar poring over primary documents, and whatever mnemonic you can come up with is good enough.

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I disagree with the accepted answer.

The all important question is what counters what.

I think 'counter' in both 'countersink' and 'counterbore' refers to the relation between primary (often cylindrical) hole and subsequently created cone or secondary bore. The secondary cone/ bore counters the primary bore. To see that, imagine what happens during creation of secondary cone/ bore. The image is that the secondary structure gradually grows in size, e.g. length, diameter, towards the primary by replacing or pushing back the latter, thus 'counter'.

'countersink' is essentially a verb. Thus 'countersunk hole', and by extension 'countersunk screw'.

'counterbore', in our context here, is often a noun, much like 'bore'. But 'to counterbore' is also used, for example, the progressive form 'counterboring'.

I don't think at all that 'counter' refers to the relation between hole (including any secondary form) and any insert. To support this, note that a cylinder head screw is never called a 'counterbore screw'. Still, it's true that the screw head has specific compatability with the (finished) hole regarding form. Indeed, you need appropriate screw for any screw hole. However, that's not the essence of 'to countersink' or 'counterbore'. The latter terms are about the relation between primary and secondary hole structure (or creation process), as opposed to hole-insert relation. ('countersunk screw' simply means 'screw appropriate for countersunk hole'. It is the hole itself that's created, in part, by countersinking or counterboring.)

As time goes by, I'll add further evidence to support my theory.

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  • But answers on ELU are expected to show supporting references or compelling data. 'I think' and 'I don't think' are conjecture. OED admittedly isn't all that convincing here, but the usage panel is made up of able linguists and they do look at the historic appearance of the sense. Commented Jul 20 at 22:51
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The accepted answer is correct.

To clarify term "countersink" for surfaces, screws, bolts, and holes:

OED

Countersink (v.)

  1. transitive. To enlarge the upper part of (a hole or cavity), usually into a conical form, to receive the head of a screw, bolt, etc.; to bevel the edge of a hole.

1831 The practice of countersinking the holes, to receive the nail heads. J. Holland, Treatise Manufactures in Metal (Cabinet Cycl.) vol. I. 170

  1. To sink the head of (a screw, bolt, etc.) in a depression made to receive it, so that it lies flush with the surface.

1815 The heads of the bolts must not project above the surface of the plate; therefore the grooves must be..wider at the top than the bottom, and the heads may then be countersunk. J. Smith, Panorama of Science & Art vol. I. 70

Countersink (n.)

  1. The conical enlargement of the upper part of a hole for receiving the head of a screw or bolt. Cf. countersunk adj. Hence countersink bit, a bit for cutting a countersink.

1879 Punching..has..the advantage of giving a slight countersink, or conical form to the hole. Cassell's Technical Educator (new edition) vol. IV. 135

Thus we can screw a countersunk (adj.) screw into the countersink (n. = conical depression) that has been made to a hole that has been countersunk (verb.)

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