: a bit or drill for making a funnel-shaped enlargement at the outer end of a drilled hole
2
: the enlargement made by a countersink
Illustration of countersink
countersink 1
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Verb
Use a nail punch if needed to countersink the nails.—Brandee Gruener, Southern Living, 25 Sep. 2025 Use a combination drill bit/countersink to bore pilot holes in the shelf and top, then drive screws to fasten them in place [12/13].—Neal Barrett, Popular Mechanics, 5 June 2021 Lay out the holes first and drill and countersink them.—Popular Science, 9 Aug. 2020
Noun
Pull out a screw, then use the countersink bit to drill out the hole.—Brandee Gruener, Southern Living, 13 Oct. 2025 This set of countersink drill bits includes five different sizes, as well as a rotating depth stop to prevent any accidental damage to your workplace.—Alex Rennie, Popular Mechanics, 2 Dec. 2022 One of the key features to notice is how the movement bridge beveling varies in its proximity to the countersinks – everything from relatively distant, to just barely touching at their exact edges, to actually flowing across a countersink proper.—Jack Forster, Bloomberg.com, 20 Jan. 2021 If screw heads sit slightly above the surface, remove, countersink, and screw back in.—The Editors Of House Beautiful, House Beautiful, 11 Feb. 2015