| http://www.w3.org/ns/prov#value | - In the fourth groove machining step for machining grooves on the face to be machined of the thin plate P to produce the grooved plate, the second protection plate 12 is disposed on a quarter of the area on the left side including the left edge and the center of the thin plate P to cover the machined area of the straight grooves 3 as shown in FIG. 6.
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