A device is provided for use with a reference tool during the construction of metal structures. The device comprises a body having a groove formed therein for receiving a portion of a straight side of the reference tool. The body further comprises a base surface for co-operating with the surface of a metal workpiece. The base surface is configured whereby, when a portion of the straight side is received within the groove, the base surface is parallel to the straight side of the reference tool. A retention assembly is mounted on the body for retaining the portion of the straight side of the reference tool, when provided, within the groove. At least one magnet is mounted on the base surface for temporarily holding the device to the metal workpiece, thereby holding the reference tool in position.