| 摘要 |
An extension for a ground boring tool ie. a Kelly shaft, comprises a hollow cylinder, closed at the bottom and provided with grips on the inside to secure to the bottom end of the telescopic extension shaft. The shaft grips the extension at different levels and when the shaft is retracted the extension slides over the telescoped shaft to lift the boring head (3) out of the bore to shake off the soil. The extension is coupled to and from the shaft by a simple bayonet action operated by the shaft drive.
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