What's the difference between curved-jaw and straight-jaw locking pliers?

Curved-jaw locking pliers grip round and irregular objects like pipes, bolt heads, and rounded fasteners with multiple contact points, while straight-jaw versions hold flat stock and sheet metal more evenly. Many users keep both styles; several of the sets here, including the multi-piece Irwin and WORKPRO kits, bundle a mix so you're covered for both jobs.