The D21 was introduced in 1963 as the largest tractor in the D Series. It used a large six-cylinder diesel, power steering, an independent 1,000-rpm PTO, and the size and weight needed for large field work.
The D21 was built from 1963 through 1969 in Series I and Series II versions. The serial number table shows the change from Series I to Series II during the 1965 production run.
Serial number locations: The tractor serial number is stamped on the left side, on the front flange of the torque housing near the starter mounting. The engine serial number is stamped on a plate at the upper rear of the engine block on the left-hand side.
The table below shows the beginning tractor serial number for each Model D21 year and series:
| Model D21 year | Beginning serial number |
|---|---|
| 1963 - Series I | 100 |
| 1964 - Series I | 1,417 |
| 1965 - Series I | 2,079 |
| Model D21 year | Beginning serial number |
|---|---|
| 1965 - Series II | 2,130 |
| 1966 - Series II | 2,408 |
| 1967 - Series II | 2,863 |
| Model D21 year | Beginning serial number |
|---|---|
| 1968 - Series II | 3,777 |
| 1969 - Series II | 4,498 |
Total production: 2,409 Model D21 tractors.
