| 摘要 |
A drill bit assembly having a housing that has an outer diameter, an inner diameter and a distal radial shoulder extending therebetween at a distal end of the housing. A first drill bit has an outer diameter and an inner diameter, wherein the first drill bit outer diameter is less than the housing inner diameter. The first drill bit includes a shank portion that is mounted within the housing inner diameter and a drill portion that extends from the shank portion and axially protrudes from the distal radial shoulder of the housing. A second drill bit has an outer diameter that is less than the first drill bit inner diameter. The second drill bit includes a shank portion that is mounted within the first drill bit inner diameter and a drill portion that extends from the shank portion and axially protrudes from a distal end of the first drill bit. The first drill bit outer diameter is larger than the second drill bit outer diameter.
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