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

1. 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.

2. 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.

3. 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.