A defect appearing as a seam on a rolled bar. Laps
are rolled over pieces of material that arise when a
bar is given a pass through the rolls after a sharp
overfill or fin has been formed, causing the
protrusion to be rolled into the surface of the
product. The presence of oxides usually prevents
the lap welding to the original bar surface, so that
in subsequent cold working it is carried through as
a longitudinal crack.