Abstract: A security device for locking or securing building material in a bundle to deter potential thieves is disclosed. The lock includes a pair of clamping elements which are adapted to be positioned at either side of a stack or bundle of material. Each of the clamping elements includes a base plate and an oppositely disposed clamping plate mounted on a shaft. The clamping plate may be vertically moved along the shaft so that the bundle is compressed between the base and clamping plate. Projections or teeth are provided on the base and clamping plate to grip the surface of the upper and lower sheet of material in the bundle. The clamping plate is lockable in any desired position once it is set. The chain or retaining cable may be extended through rings provided on the clamping plate between the oppositely positioned clamping elements to further discourage unauthorized removal of the clamping elements.