US PATENT SUBCLASS 175 / 243
.~ Resiliently biased or composed of flexible material

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

232  DF  WITH MEANS MOVABLE RELATIVE TO TOOL BELOW GROUND TO STOP FLOW TOWARD BORE BOTTOM {8}
243.~ Resiliently biased or composed of flexible material

DEFINITION

Classification: 175/243

(under subclass 232) Apparatus in which (1) the movable means is held in a position by a resilient means such as spring or (2) the movable means is composed for flexible material such as rubber (e.g., flap valve).