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- Provides gripping power on two sides of the head with another side open so the wrench can be placed on a nut, which might not be accessible to a closed or box wrench.
- Has different size openings on each end and should fit the nut exactly to prevent mutilating the nut edges.
- Some types, called flare nut wrenches, are flared to fit hex fittings and flare nuts.
- Generally available in sets.