| 摘要 |
PROBLEM TO BE SOLVED: To prevent twisting and deformation from generating even when a load is applied to the base plate, and keep a uniform strength by a method wherein at a plurality of locations between a large number of circular bowl-shaped protuberances when being seen from the top, a circular rib when being seen from the top, having a dimension which is substantially shallower than the depth dimension of the bowl- shaped protuberance, is integrally formed on the lower surface of a square flat base plate. SOLUTION: A square flat base plate 1 comprises a metal plate, e.g. a steel plate, or a hard synthetic resin. On the lower surface of the square flat base plate 1, nine circular bowl-shaped protuberances 2 having the same depth dimension, are formed in the longitudinal and lateral directions while being respectively aligned with equal intervals. At a plurality of locations between the nine circular bowl-shaped protuberances when being seen from the top, four circular ribs 3 when being seen from the top, having a dimension t2 which is substantially shallower than the depth dimension t1 of the bowl-shaped protuberance 2, are integrally formed. Also, the diameterϕ2 of the rib 3 is made larger than the diameterϕ1 of the bowl-shaped protuberance 2. By this structure, the durability is high, and a uniform strength can be obtained, and twisting and distortion can be prevented from generating.
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