A fastener and associated lock washer having an integral anti-rotation mechanism. The head of the fastener includes a plurality of saw teeth—arranged in a radial array. A lock washer is configured to interact with the head of the fastener. The lock washer includes one or more spring tabs positioned to bear against the radial array of saw teeth. As the fastener is rotated in a first direction, the saw teeth depress and pass over the spring tab(s). However, if the user attempts to rotate the fastener in the opposite direction, the spring tab snaps up into the saw teeth and arrests the motion—in the manner of a ratchet and pawl mechanism. The invention preferably includes a second means for selectively defeating the anti-rotation mechanism.