Holds up rafters and joists, eliminating the need for two people. Automatically levels the crossmember with the rimjoist or ledger giving the framer a "hands free" position while installing the joist hanger or other connectors. Clamps down on target fromthe top or the bottom and holds lumber tight. Reusable and made of zinc plated durable steel. For all 2x wood framing or less. Decking, roofing, and flooring applications. Includes 2 joist jaws per package.