| 摘要 |
A casing having a boot heel engaging means at its front end is pivoted to a connecting member which is mounted on a base. The connecting member comprises a transverse horizontal plane at its front end and a longitudinal bore which lower end is on the same level as the horizontal plane. Within the longitudinal bore a locking member is provided to be urged forwards which has at its front surface a dented portion to engage with a horizontal pin secured to the casing in the boot heel engaging position.
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