C7, C5 and C3 are accuracy grades that define the lead error of a ball screw over a reference length. They do not directly define backlash. You can think of them like this:
Process: Usually cold-rolled (rolled ball screw), lowest cost.
Lead accuracy: Typical tolerance is around ±0.05 mm per 300 mm travel (exact value depends on the standard and manufacturer).
Best suited for:
3D printers and hobby CNC
Wood routers and basic engraving machines
Handling modules, packaging machines and general automation where ±0.1–0.2 mm over the stroke is acceptable
Backlash note: Most C7 screws are supplied with a standard single nut that has some clearance.
If you require minimal backlash, you must choose a preloaded nut (oversized balls) or a double-nut design. Upgrading from C7 to C5 alone does not magically remove backlash.
Process: Traditionally, C5 is ground and significantly more expensive than C7 (often 3–5*).
Lead accuracy: Around ±0.018 mm per 300 mm travel (depending on standard/manufacturer).
Best suited for:
Industrial CNC milling and turning machines
Precision positioning axes in automation
Applications that need tighter dimensional control over long strokes
Benefits:
Better lead accuracy and repeatability
Smoother running and lower noise compared to many rolled C7 products
Middle option: There are now C5 rolled ball screws on the market which offer better accuracy than standard C7 with a lower price than fully ground C5. For many machines, this is a good compromise between cost and performance.
Process: High-end ground ball screws, often with strict temperature control during manufacturing.
Lead accuracy: Around ±0.008 mm per 300 mm.
Best suited for:
Jig grinders and high precision grinding machines
Semiconductor equipment
Coordinate measuring machines (CMM) and ultra-precision positioning systems
Accuracy grade ≠ zero backlash
C5 tells you the screw “walks the right distance" (lead accuracy).
It does not guarantee that there is no axial play when you reverse direction.
If you care about lost motion / backlash, you must specify a preloaded nut or double-nut solution. This is often more important for feel and positioning at reversal than the difference between C7 and C5 grades.
Long travel and cumulative error
The often-quoted accuracy values (e.g. per 300 mm) are per segment, not for the entire axis.
On a 1 m or longer axis, C7 lead error can accumulate to several tenths of a millimeter.
If your axis is long and you need parts to fit accurately over that whole length, you should seriously consider C5 (or at least a higher-accuracy rolled option) even if you don’t need the absolute smoothness of ground C5.
How to choose in practice
C7 rolled – when budget is limited and your acceptable error is in the ±0.1–0.2 mm range over the stroke. Combine it with a preloaded nut if you want less backlash.
C5 (ground or high-accuracy rolled) – when you build serious CNC equipment or long-travel axes that need better dimensional accuracy and smoother motion.
C3 ground – only when you clearly need high-end precision and your machine structure, feedback system and temperature control can actually take advantage of that grade.
