The wheel on which the rope works in a block; it is generally formed of lignum vitæ, sometimes of brass, and frequently of both; the interior part, or that which sustains the friction against the pin, being of brass, let into the exterior, which is of lignum vitæ, and is then termed a sheave with a brass coak, bouche, or bush. The name also applies to a cylindrical wheel made of hard wood, movable round a stout pin as its axis; it is let through the side and chess-trees for leading the tacks and sheets. Also, the number of tiers in coiling cables and hawsers.