Abstract: A masonry line stretching apparatus which has a body (20) of cast aluminum material with an integral upright finger (24) and lower jaw (32). A slideable jaw (40) is positioned on the body and is free to be adjustably moved relative to the lower jaw. A stop (52) retains the slideable jaw and the device is used in pairs with the jaws being adjusted into a gripping position on a building block (38) in the form of a brick (44) or concrete block (48). A masons line (36) is strung between two of the apparatus positioned adjacent to corner building blocks allowing the mason to maintain a straight row or face during the construction process. The device may be used with the body disposed on top of the block or opposite with the body cantilevered therefrom. The jaws grip either the entire block, in the case of a brick, or from the opening (46) to the edge, in the case of a concrete or cinder block (48).