PURPOSE: To prevent occurrence of danger and generation of rust by covering whole face on both sides of a metallic plate on which many long slender holes are made in a fixing direction with a rust preventive film and spreading the long holes to circular form by pulling the metallic plate in the direction of minor axis of the long holes and covering the edges of holes with the film.

CONSTITUTION: Many long holes 2 are made on a metallic plate 1 regularly at fixed intervals and in a fixed direction. Next, whole face of both sides of the metallic plate 1 and long holes are covered with a rust preventive film 3. Then, the metallic plate 1 is pulled in the direction of minor axis of the long holes 2 to spread the long holes from oblong form to nearly circular form. At this time, the long holes 2 are pulled by tensile deformation of the metallic plate 1, and the rust preventive film 3 is torn in the direction of major axis of te long holes. Thus, the film covers the edges of the long holes 2 without peeling from the metallic plate 1 and protects whole faces on both sides of the wire net.