175 / | HD | BORING OR PENETRATING THE EARTH |
293 | DF | BELOW-GROUND (1) HAMMER, OR (2) IMPACT MEMBERS {7} |
300 | .~ With releasable means to detachably retain telescoping members against axial reciprocation {3} | |
301 | DF | .~.~> Frangible |
302 | DF | .~.~> Condition for release adjustable {1} |
304 | DF | .~.~> Resiliently biased latch |