third elastic plate portion 20 h the surfaces of the first elastic plate portion 20 a the third elastic plate portion 20 h and the second elastic plate portion 20 b cross each other at right angles to form a crisscross spring 21 an extension 20 c from one end of the first elastic plate portion 20 a is bent at 45 u00b0 from the first elastic plate portion 20 a while an extension 20 d from the other end of the first elastic plate portion 20 a is bent at 135 u00b0 from the first elastic plate portion 20 a an extension 20 e from one end of the second elastic plate portion 20 b is bent at 135 u00b0 from the second elastic plate portion 20 b while an extension 20 f from the other end of the second elastic plate portion 20 b is bent at 45 u00b0 from the second elastic plate portion 20 b further an extension 20 j from one end of the third elastic plate portion 20 h is bent at 45 u00b0 from the third elastic plate portion 20 h while an extension 20 k shown in fig5 referred to below from the other end of the third elastic plate portion 20 h.