| 3/00 | Firebridges (baffles not confining the fire F23M 9/06) |
| 3/02 | Firebridges (baffles not confining the fire F23M 9/06) modified for circulation of fluids, e.g. air, steam, water |
| 3/04 | Firebridges (baffles not confining the fire F23M 9/06) modified for circulation of fluids, e.g. air, steam, water for delivery of gas, e.g. air, steam |
| 3/06 | Firebridges (baffles not confining the fire F23M 9/06) modified for circulation of fluids, e.g. air, steam, water for delivery of gas, e.g. air, steam into or towards fire |
| 3/08 | Firebridges (baffles not confining the fire F23M 9/06) modified for circulation of fluids, e.g. air, steam, water for delivery of gas, e.g. air, steam away from fire, e.g. towards smoke outlet |
| 3/10 | Firebridges (baffles not confining the fire F23M 9/06) modified for circulation of fluids, e.g. air, steam, water for delivery of gas, e.g. air, steam transversely |
| 3/12 | Firebridges (baffles not confining the fire F23M 9/06) characterised by shape or construction (F23M 3/02 takes precedence) |
| 3/14 | Firebridges (baffles not confining the fire F23M 9/06) characterised by shape or construction (F23M 3/02 takes precedence) with apertures for passage of combustion products |
| 3/16 | Firebridges (baffles not confining the fire F23M 9/06) characterised by shape or construction (F23M 3/02 takes precedence) built-up in sections, e.g. using bars or blocks |
| 3/18 | Firebridges (baffles not confining the fire F23M 9/06) characterised by shape or construction (F23M 3/02 takes precedence) double; multiple |
| 3/20 | Firebridges (baffles not confining the fire F23M 9/06) characterised by shape or construction (F23M 3/02 takes precedence) comprising loose refractory material, wholly or in part |
| 3/22 | Firebridges (baffles not confining the fire F23M 9/06) movable; adjustable |
| 5/00 | Casings; Linings; Walls (casings, linings, or walls of heat-treatment chambers of ovens, kilns, or retorts F27D) |
| 5/02 | Casings; Linings; Walls (casings, linings, or walls of heat-treatment chambers of ovens, kilns, or retorts F27D) characterised by the shape of the bricks or blocks used (ceramic materials C04B 33/00, C04B 35/00) |
| 5/04 | Casings; Linings; Walls (casings, linings, or walls of heat-treatment chambers of ovens, kilns, or retorts F27D) Supports for linings |
| 5/06 | Casings; Linings; Walls (casings, linings, or walls of heat-treatment chambers of ovens, kilns, or retorts F27D) Crowns or roofs for combustion chambers (F23M 5/02, F23M 5/04 take precedence) |
| 5/08 | Casings; Linings; Walls (casings, linings, or walls of heat-treatment chambers of ovens, kilns, or retorts F27D) Cooling thereof; Tube walls |
| 7/00 | Doors specially adapted for combustion chambers (in general E06B; for flues or smoke-boxes F23J 13/08) |
| 7/02 | Doors specially adapted for combustion chambers (in general E06B; for flues or smoke-boxes F23J 13/08) Frames therefor |
| 7/04 | Doors specially adapted for combustion chambers (in general E06B; for flues or smoke-boxes F23J 13/08) Cooling doors or door frames |