US PATENT SUBCLASS 454 / 33
.~.~ Spiral or plural stacked rings

Current as of: June, 1999
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454 /   HD   VENTILATION

1  DF  CHIMNEY OR STACK {6}
3  DF  .~ Chimneytop or stacktop structure (e.g., cowl) {12}
33.~.~ Spiral or plural stacked rings

DEFINITION

Classification: 454/33

Spiral or plural stacked rings:

(under subclass 3) Subject matter wherein the structure comprises (1) spaced-apart, helically-arranged strips or (2) rings spaced apart and positioned one above another.