the.com/nail set

A tiny metal punch whose only job is to make nails disappear below the surface.

means A small hand tool with a cupped or dimpled tip, used with a hammer to drive nail heads just below the wood surface so the hole can be filled.

from A plain compound of 'nail' plus 'set' — this 'set' being the old carpentry sense of driving something firmly into place, as in 'to set a nail.' The tool itself traces to simple blacksmith-made punches, its name describing its job rather than any clever wordplay: it sets nails below the surface, end of story.

actual use
sinks nail heads below wood so filler can hide them
tip shape
concave cup grips the nail head so it doesn't slip
size matters
comes in several tip widths matching different nail sizes
cheap genius
costs almost nothing but saves finish carpentry from hammer dents
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