The drill bit in a cone shape outside has an outer diameter larger than or equal to the drill barrel to form an outer bulge.
钻头外侧呈锥体形状，钻头外径大于或等于钻筒外径形成外凸。
The drill bit in a cone shape outside has an outer diameter larger than or equal to the drill barrel to form an outer bulge.
钻头外侧呈锥体形状，钻头外径大于或等于钻筒外径形成外凸。
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