Accuracy class is about lead error
Ball screw accuracy class is defined by lead error, not just shaft diameter. C3, C5, and C7 are the three most common classes on the market: the smaller the number, the smaller the lead error, the higher the accuracy, and the higher the price. In practice, C5 and tighter classes are usually ground ball screws, while C7 is commonly rolled, which is why a "C5 ground ball screw" and a rolled C7 differ in both accuracy and cost.
- C7: larger lead error, suitable for ordinary CNC, woodworking machines, and general automation.
- C5: clearly better accuracy, suitable for machining centers, mold equipment, and precision positioning.
- C3: high accuracy for measuring equipment, high-end machining, and laboratory instruments.
Choose the class by positioning requirement
Before choosing, ask what positioning accuracy the machine actually needs. Ordinary woodworking CNC works with C7, machining centers use C5, and precision engraving or measuring equipment needs C3. Accuracy you will not use only adds cost and lead time.
Accuracy is not the only factor
Besides the class, confirm nut preload (to remove backlash), screw support arrangement (fixed-support or fixed-fixed), and installation and adjustment. Without enough preload, even a C5 screw can show backlash.
State acceptance in the RFQ
- Accuracy class: C5 or C7, noted in the model.
- Acceptance criteria: lead error, axial clearance, and runout checks.
- Inspection report: whether factory measurement data travels with the goods.
- Installation: on-site installation or self-assembly.
FAQ
How much more does C5 cost than C7?
Generally 20%-50% more, depending on specification and process; the gap grows with thicker screws. Ask for a quotation by model for an exact price.
Can the inspection report show accuracy?
Yes. The factory report lists lead error, runout, and preload data, which you can compare with the stated class to judge acceptance.
Next step
Turn this guide into an RFQ
When the specification direction is clear, send the details below together with quantity, lead time, and packing requirements.
Include these details
- Model, diameter, lead, accuracy grade, or target application.
- Load, speed, travel, mounting method, and matching rail or support-unit needs.
- Quantity, lead time, packing, and whether inspection records or shipment photos are needed.
Category
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