Two or more spars, raised at angles, lashed together near their upper ends, and supported by guys; used for raising or taking in heavy weights. Also, to hoist in or get out the lower masts of a ship; they are either placed on the side of a quay or wharf, on board of an old ship cut down (see sheer-hulk), or erected in the vessel wherein the mast is to be planted or displaced, the lower ends of the props resting on the opposite sides of the deck, and the upper parts being fastened together across, from which a tackle depends; this sort of sheers is secured by stages extending to the stem and stern of the vessel.