A method and apparatus comprising a structure and a locking magnet. The structure comprises a retaining portion and a magnetic portion. The retaining portion of the structure is configured to receive a first section of a workpiece such that a second section of the workpiece is positioned at an angle relative to the magnetic portion of the structure. The magnetic portion of the structure is positioned at a first side of the workpiece. The locking magnet is configured to exert an attractive force that causes the magnetic portion of the structure to move towards the second section of the workpiece when the locking magnet is positioned at a second side of the workpiece.