A fi is a conical tool made of wood or bone. It is used to work with rope and canvas in marlinespike seamanship. A fid differs from a marlinspike in material and purpose. A marlinespike is used in working with wire rope, may be used to open shackles, and is made of metal. A fid is used to hold open knots and holes in canvas. A fid is used to open the "lays", or strands of rope, synthetic or natural, for splicing said line.