US PATENT SUBCLASS 175 / 390
.~.~.~ Plural larger diameter steps

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

327  DF  BIT OR BIT ELEMENT {21}
385  DF  .~ Bit with leading portion (e.g., pilot) forming smaller diameter initial bore {6}
389  DF  .~.~ Impact type {1}
390.~.~.~ Plural larger diameter steps

DEFINITION

Classification: 175/390

(under subclass 389) Apparatus in which the cutting edges of the impact bit are arranged so that the boring outline of the bit will describe at least two peripheral axial steps.