| 摘要 |
A barrel has a longitudinal shaft (c), a pair of controlling plates (10) are arranged in a symmetry relative to longitudinal axis, a pair of oil grooves (3) are formed spirally about the axis within the barrel. The oil groove has an inlet in symmetry to the longitudinal axis at the upper part of the barrel. The grooves respectively have an outlet in symmetry to the longitudinal axis at the bottom part of the barrel. A hole provided at a knob of inclined controlling plate is to engage with the plate (10) to securely fix the plate on the body.
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