| 165 / | HD | HEAT EXCHANGE |
| DIG 510 | DD | HAVING HEAT EXCHANGE SURFACE TREATMENT, ADJUNCT OR ENHANCEMENT {7} |
| DIG 518 | DD | .~ Conduit with discrete fin structure {5} |
| DIG 522 | DD | .~.~ Transverse fins spaced along conduit {1} |
| DIG 523 | | .~.~.~ Separated by integral flanges engaging conduit exterior |