jack leg是什么意思

用法例句

A dismantling and assembling machine for four-leg drill derricks and a mechanically assembleddrill derrick have been developed, which are thought to the trend of the geologic drill derrick.

指出了目前钻塔拆装存在的缺点，提出了解决的新途径，研制成功了四腿钻塔拆装机及机装可逆式四腿管子钻塔，认为这是地质钻塔发展的新方向。