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A flat-bottomed bracket shape, calling for a flat-bottomed enlarged hole.
Also known as: Spotface symbol, Square bracket on a drawing, U shape drawing symbol
A square-bottomed bracket calls for a counterbore: a flat-bottomed widening so a bolt head sits below the surface. Its near-twin, the countersink, is a V — and the shape of the symbol is a picture of the hole.
Calls for a flat-bottomed cylindrical enlargement of a hole, so a bolt head or nut sits at or below the surface.
Contexts: Technical drawing
Is drawn as a picture of the resulting hole in section, which is why the counterbore is square-bottomed and the countersink a V.
Contexts: Technical drawing
Two short vertical strokes joined at the bottom by a horizontal one, forming a squared-off U open at the top.
Both are small bracket-like marks before a hole dimension; square bottom against V bottom.