| F | SK | MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING |
| F27 | KL | FURNACES; KILNS; OVENS; RETORTS (specially adapted for a purpose covered by a single other class and specifically mentioned in that class, see the class in question, e.g. bakery ovens A21B , glass melting furnaces C03B , coke or gas-making apparatus C10B , C10J , apparatus for cracking hydrocarbons C10G , blast furnaces C21B , converters for making steel C21C , furnaces for heat treatment of metal C21D; furnaces for electroslag or arc remelting of metals C22B 9/00; enamelling ovens C23D; combustion apparatus F23; electric heating H05B) [4] |
| F27B | UKL | FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS |
| F27D | UKL | DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE (combustion apparatus F23) |