The spring member 4 is made of poly-phenylene oxide and is formed to a nearly U sectional shape and further top end parts of parts 4a extending in parallel and facing each other are in contact with the both clamping plates 3a, 3b in a state extending till near top end parts of the clamping plates 3a, 3b. バネ部材4はポリフェニレンオキシド製で断面ほぼU字状に形成されるとともに、その対向して平行に延びる部分4aの先端部が挟持板3a,3bの先端部近傍まで延びる状態で両挟持板3a,3bに当接している。 - 特許庁