Picking the right replacement disc blade comes down to four measurements — nail those and everything else falls into place. This guide walks you through each in the order you should confirm them.
1. Diameter
Measure the outside diameter of your worn blade in inches. Disc harrow blades come in a specific set of sizes: 14", 16", 18", 20", 22", 24", 26", 28", 30", 32", 36", and larger. If your blade is worn down enough to be smaller than the original, look up the original diameter in your machine's manual or match to the mount hole spacing.
Common pairings by machine class:
- Light-duty disc harrows (residential, small garden): 16"-20"
- Standard farm disc harrows: 20"-24"
- Heavy-duty offset discs: 24"-28"
- Vertical tillage / high-speed disks: 20"-24" (thinner, faster rotation)
2. Thickness
The second-most important spec after diameter. Thickness is measured in millimeters (metric) or fractions of an inch. Common thicknesses:
| Metric | Fraction | Typical use |
|---|---|---|
| 4.5 mm | 3/16" | Light-duty, small acres |
| 6 mm | 1/4" | Standard field cultivator / disc harrow |
| 6.5 mm | — | Standard heavy tillage |
| 8 mm | 5/16" | Heavy offset / rocky ground |
| 10 mm | 3/8" | Extreme heavy-duty, dry-hard soil |
Thicker blades last longer but add weight to the machine and demand more tractor HP. If your soil is soft and you're not fighting rocks, don't over-buy.
3. Axle bore
The hole in the center of the blade needs to match the axle it slides onto. Two shapes exist:
- Square axle — most disc harrows. Common sizes: 1", 1-1/8", 1-1/4", 1-1/2", 2".
- Round axle — some older or specialty rigs. Common: 1-3/4", 2".
Measure diagonally corner-to-corner for square axles. If the old blade is on a spool with bushings, verify the actual axle size, not the bushing OD.
4. Edge (notched or smooth)
Choose based on residue and soil conditions — see our Notched vs. Smooth guide for the full breakdown.
Quick order checklist
- Diameter (inches)
- Thickness (mm or fraction)
- Axle bore (size and shape)
- Edge (notched or smooth)
- Number of blades needed
If you can send us those five specs, we can quote you the same day. Call 641-425-8034 or email sales@discbladesforsale.com.