US PATENT SUBCLASS 181 / 280
.~.~.~.~ Helical

Current as of: June, 1999
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181 /   HD   ACOUSTICS

175  DF  SOUND-MODIFYING MEANS {12}
212  DF  .~ Muffler, fluid conducting type {25}
264  DF  .~.~ With baffle or baffle structure {9}
279  DF  .~.~.~ Spiral {1}
280.~.~.~.~ Helical

DEFINITION

Classification: 181/280

Helical:

(under subclass 279) Subject matter in which the circular path is axially expanding.