| NSB Class XXI | |
| Powertype: | Steam |
| Builder: | Dübs & Co. (2) Thunes Mekaniske Værksted (1), Hamar Jernstøberi (1) |
| Serialnumber: | Dübs 3172–3173, Thune 4, Hamar 77 |
| Builddate: | 1894 (2), 1901 (1) 1912 (1) |
| Totalproduction: | 4 |
| Whytetype: | 2-6-2T |
| Uicclass: | 1′C1′t n2 |
| Driverdiameter: | 914mm |
| Minimumcurve: | 100m (300feet) |
| Length: | 8300mm |
| Weightondrivers: | 14.7 t |
| Locoweight: | 18.7 t |
| Fueltype: | Coal |
| Fuelcap: | 800NaN |
| Watercap: | 2.1 t |
| Boilerpressure: | 145psi |
| Firearea: | 0.7m2 |
| Totalsurface: | 407.6square feet |
| Cylindercount: | Two, outside |
| Cylindersize: | 11x or 11.5x |
| Maxspeed: | 40km/h |
| Locobrakes: | Hand brake, Carpenter brake from 1900 |
| Operator: | Norwegian State Railways |
| Fleetnumbers: | 1, 2, 5, 7 |
| Locale: | Setesdal Line |
NSB Class XXI is a steam locomotive class designed by the Norwegian State Railways exclusively for use on the Setesdal Line.[1]