| Nickname: | Donnerbüchse |
| Owner (company): | Deutsche Bundesbahn |
| Type: | Zweiachsiger Einheits-Durchgangswagen |
| Label: | Bi-21 |
| Category: | Passenger coach |
| Era: | 3a |
| Overall length: | 13920 mm |
| Wheelbase: | 8500 mm |
| Weight: | 20000 kg |
| Weight / Number of Seats: | 500 kg |
| Seat: | 40 |
| Interiour arrangement: | Saloon, central corridor |
| Maximum speed: | 90 km/h |
| Made in (Year): | 1921-1923 |
| Amount: | (10) |
| Brake: | Kkpbr (Klotz) |
| Heating system: | Steam, low pressure, circulation |
| Lighting: | Electric |