middle hole meaning in Chinese

中洞

Pull the servo extension cord out of the middle hole above the wing , for later use
舵机延长线从机翼上面中部的孔中用预留的线绳拉出备用。
The current transformer is busbar type . the secondary windings and iron core are insulated by epoxy resin . the middle hole is used for busbar going through and mounting
本型电流互感器为母线式。二次绕组及铁芯均浇注在聚脂树脂内，中间窗孔供一次母线穿过及安装用。
The current transformer is busbar type . the secondary windings and iron core are enclosed in a plastic crust . the middle hole is used for busbar going through and mounting
本型电流互感器为母线式。二次绕组及铁芯均封装在阻燃塑料壳内，中间窗孔供一次母线穿过及安装用。
The zero sequence current transformer is full enclosed type . the secondary windings and iron core are insulated by epoxy resin . the middle hole is used for cable going through
本型零序电流互感器为全封闭式。二次绕组及铁芯均浇注在聚脂树脂内。中间窗孔供三相电缆穿过。