Abstract: A tool is provided for preventing bolts from turning while the nut on the bolt is being loosened or tightened. The tool comprises opposed handle members each operatively connected to a jaw. The first jaw comprises a central longitudinally extending member designed to engage the head of a bolt when the tool is locked in place. The second jaw comprises a U-shaped member having two forked portions positioned on opposite sides of the plane of the first jaw member and being spaced apart sufficiently to receive the nut of a bolt therebetween when the tool is locked in place. Adjustable, releasable locking means are provided for locking the tool in place so as to prevent backout of the bolt while the nut on the bolt is being loosened or tightened.