US PATENT SUBCLASS 175 / 294
.~ Combined with safety joint

Current as of: June, 1999
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175 /   HD   BORING OR PENETRATING THE EARTH

293  DF  BELOW-GROUND (1) HAMMER, OR (2) IMPACT MEMBERS {7}
294.~ Combined with safety joint

DEFINITION

Classification: 175/294

(under subclass 293) Apparatus combined with a joint between two parts which may be selectively uncoupled below ground independently of other joints in the apparatus, such that one part may be left in the bore while the other part is withdrawn therefrom.