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.

Guides that use

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