The head of a ring spanner encircles a nut completely; it is generally 12-pointed in shape (often referred to as bi-hex) and will locate on a square or a hexagonal nut with a very secure grip.

Because the spanner cannot slip, it allows the maximum turning pressure to be applied, and should be used wherever possible to slacken a nut. But it can be used only where there is access over the top of the nut, and cannot be used to undo nuts on pipe unions, for example.

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