Ball Screw Precision Grade — C3 / C5 / C7 / C10 Explained

Ground vs rolled ball screws and the real meaning of C3, C5, C7 and C10 accuracy classes, with per-300 mm runout numbers to pick the right grade.

1. Ground vs rolled

Ground (precision-ground) screws are finished by grinding the raceway to a tight tolerance — high accuracy, small backlash, higher cost. Rolled screws are formed by thread rolling — economical, good for general automation where extreme accuracy is not required.

2. Accuracy classes (runout per 300 mm)

Grade	Runout / 300 mm	Process	Use
C3	≈ 0.008 mm	Ground	Semiconductor, measuring instruments, high-end CNC
C5	≈ 0.018 mm	Ground	CNC machining centres, laser processing
C7	≈ 0.050 mm	Rolled	General automation, lifting, feed
C10	≈ 0.210 mm	Rolled	Rough positioning, low-cost transport

Figures are MOSIONX typical values; confirm against the specific catalog model.

3. How to choose

If the machine must hold a position to a few microns → ground C3/C5.
If it only needs repeatable, non-critical feed → rolled C7 is enough and much cheaper.
Backlash-sensitive axes benefit from a preloaded (double-nut) ground screw.

4. Related technical guides

Ball Screw Selection Support Units Mounting Torque & Pre-stretch Troubleshooting Support Unit Selection