How to Choose the Right Types of Ball Screws

This article explains the main types of ball screws by manufacturing method, precision grade, ball circulation method, nut structure, and lead size. It also gives practical selection references for different industrial applications.

What a Ball Screw Actually Does - and Why Type Selection Matters

A ball screw converts rotary motion into linear motion using recirculating balls that roll between a threaded shaft and a nut. Because the balls roll rather than slide, a ball screw achieves much higher efficiency (typically 90% or above) compared to a traditional lead screw, and it does so with a much higher level of repeatability.

That said, not all ball screws are built the same way. A rolled C7 screw with a single nut and a 20mm lead behaves very differently from a ground C5 screw with a double nut and a 5mm lead - even if both have the same nominal diameter. Selecting the wrong combination can mean paying more than necessary, or selecting a screw that fails to meet accuracy or life requirements.

The sections below cover each dimension in turn.

1. Manufacturing Method: Rolled vs Ground

The manufacturing method is one of the most important ways to classify ball screws. It directly affects accuracy, cost, production time, surface quality, and suitable application range.

Rolled Ball Screw

A rolled ball screw is produced by a rolling process. The thread groove is formed by rolling dies, which makes production efficient and cost-effective. Rolled ball screws are widely used in general industrial applications because they offer stable motion performance with a more economical price.

Rolled ball screws are suitable for automation equipment, packaging machinery, woodworking machines, CNC routers, 3D printers, and general transfer or positioning systems where ultra-high lead accuracy is not required.

For DLY products, cold-rolled ball screws are generally C7 accuracy grade. They are often selected when the machine needs reliable motion, reasonable accuracy, shorter delivery, and better cost control.

Ground Ball Screw

A ground ball screw is produced by precision grinding. This process provides better lead accuracy, smoother raceway surface, and more stable motion performance for high-precision applications.

Ground ball screws are commonly used in precision CNC machines, grinding machines, inspection equipment, measuring devices, semiconductor equipment, and high-accuracy positioning systems.

For DLY products, ground ball screws are generally C5 accuracy grade. They are selected when higher positioning accuracy and better lead error control are required.

How to decide: If your application requires positional repeatability better than ±0.05mm, ground is the baseline requirement. For general automation where the positioning tolerance is ±0.1mm or wider, rolled screws offer good value without sacrificing reliability. Avoid over-specifying: a C3 ground screw running in a contaminated or poorly lubricated environment will not outperform a properly maintained C7 rolled screw.

2. By Precision Grade

Ball screw precision grade is mainly related to lead accuracy and positioning performance. Higher precision grades are used when the machine requires tighter positioning control, better repeatability, and smaller lead error.

Common ball screw accuracy grades include C0, C1, C2, C3, C5, C7, and C10. In general, the smaller the grade number, the higher the accuracy requirement and the higher the manufacturing cost.

However, higher accuracy is not always necessary. The accuracy grade should match the machine structure, guideway accuracy, bearing support, installation surface, control system, load, and working environment.

3. Ball Circulation Method: How the Balls Return

Inside a ball screw nut, the balls travel along the thread and must be continuously returned to the start of the circuit to allow uninterrupted motion. The method used to return the balls has a significant effect on the screw's speed capability, noise level, installation envelope, and suitability for different load conditions.

External Tube Circulation

Balls exit the nut through a deflector, travel through an external return tube mounted on the outside of the nut body, and re-enter the circuit at the other end. This is a robust, well-proven design that is straightforward to manufacture and service.

External tube designs handle heavy loads well because the return path geometry allows for larger ball sizes and multiple circuits. They are widely used in heavy-duty CNC axes, milling machines, and industrial presses.

The drawback is the external return tube adds to the outer diameter of the nut. On compact machine designs, this can create clearance problems.

Internal Circulation

In internal circulation designs, the balls are returned through passages machined into the nut body itself, using deflectors that redirect the balls from the end of one circuit to the beginning of the next without leaving the nut envelope.

This design results in a more compact nut with a smaller outer diameter, which is useful where installation space is tight. The internal path also tends to produce smoother, lower-noise operation at moderate speeds.

Internal circulation is commonly used in engraving machines, medical positioning systems, and compact automation modules.

End Cap Return (also called Deflector-type or High-speed)

End cap designs use precisely formed end caps at each end of the nut to redirect the balls. This geometry allows the balls to travel at higher speeds with reduced noise and vibration, and it typically achieves higher Dm·N values (a combined measure of diameter and speed) than tube or internal designs.

This is the preferred design for high-speed applications: fast-moving gantries, laser cutting machines, high-throughput pick-and-place systems. End cap designs also integrate well with wiper seals and dust protection features.

Helical Groove Return 

In helical groove designs, the return path is integrated directly into the nut body as a helical groove running parallel to the thread. This compact geometry suits miniature screws with small leads where conventional return methods are not practical.

This design is used in fine-positioning applications: small-diameter precision screws in medical devices, optical systems, and semiconductor handling equipment.

4. Nut Structure: Single Nut vs Double Nut

The ball nut structure affects backlash control, rigidity, installation space, cost, and maintenance. Common nut structures include single nut, double nut, and left/right-handed nut designs.

Single Nut Ball Screw

A single nut ball screw is the most common and economical structure. It is compact, easy to install, and suitable for many standard automation and general industrial machines.

Single nut designs are suitable when the application needs stable motion but does not require extremely high rigidity or strict backlash control.

When single nut is the right choice:

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  Standard positioning applications with moderate accuracy requirements
  Applications where a small amount of axial clearance is acceptable or compensated by the control system
  Cost-sensitive designs where double-nut stiffness is not required
  Space-constrained axes where nut length must be minimized

The SFU series is a flanged single-nut design with end cap ball return, suitable for a wide range of CNC and automation applications. It is available in diameters from 12mm to 80mm with leads from 4mm to 20mm.

Double Nut Ball Screw

A double nut ball screw uses two nuts to apply preload and improve rigidity. It is often selected when better backlash control and higher positioning stability are required.

Double nut structures are suitable for CNC machines, precision positioning axes, heavy-load systems, and applications where axial stiffness is important. They usually require more installation space and higher cost than single nut designs.

When double nut is the right choice:

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  Applications where backlash must be zero or near-zero: high-precision CNC axes, grinding machines, EDM equipment
  Axes subject to reversing loads where clearance would cause position error at the reversal point
  High-rigidity requirements where the ball screw assembly forms part of the structural load path
  Vertical axes where the weight of the load creates a sustained downward preload on the return stroke

What double nut does not fix: Preloading against backlash increases friction and generates more heat. An overloaded or insufficiently lubricated double nut will wear faster than a correctly sized single nut. Double nut selection should be based on stiffness and backlash requirements, not on the assumption that more preload is always better.

Left/Right-Handed Nut Ball Screw

A left/right-handed ball screw structure can create opposite movement directions on the same screw shaft. This design is often used in mechanisms that require synchronized opening and closing or symmetrical movement.

Typical applications include clamping devices, centering mechanisms, adjustment devices, and special automation equipment.

5. Lead Selection: Matching Speed, Force, and Resolution

Lead is the axial distance the nut travels per full revolution of the screw. It has a direct effect on three things: achievable linear speed, available thrust force, and positioning resolution.

Speed: For a given motor speed, a larger lead produces higher linear velocity. If your axis must move at 1,000 mm/s and your motor runs at 3,000 RPM, the minimum lead required is: 1,000 mm/s × 60 ÷ 3,000 RPM = 20mm.

Force: For the same motor torque, a smaller lead produces higher thrust. A 5mm lead screw produces four times the thrust of a 20mm lead screw driven by the same motor, because the mechanical advantage is greater.

Resolution: A smaller lead means finer positioning per motor step or encoder count. This matters in applications where the control system's resolution must be tight.

Small Lead Ball Screw

Small lead ball screws usually have a lead below 5 mm. They are suitable for applications that require fine positioning, high thrust, and better control at lower speed.

Typical applications include precision adjustment, Z-axis lifting, medical equipment, laboratory instruments, and small positioning stages.

Medium Lead Ball Screw

Medium lead ball screws usually have a lead between 5 mm and 20 mm. They provide a balance between speed, thrust, and positioning accuracy.

This type is widely used in CNC machines, automation equipment, packaging machinery, woodworking machines, and general industrial motion systems.

Large Lead Ball Screw

Large lead ball screws usually have a lead above 20 mm. They are used when high linear speed is required.

Large lead screws are suitable for high-speed transfer, long-stroke feeding, loading and unloading systems, and fast automation axes. However, positioning resolution and thrust should be checked carefully when using a larger lead.

Important consideration for vertical axes: On a vertical axis, gravity acts continuously on the load. A large-lead screw may back-drive under gravity when the motor is not holding torque - this is a physical property of the lead geometry, not a defect. Any vertical axis using a lead above approximately 10–12mm should be evaluated for back-driving risk, and if back-driving is a concern, the design must include a motor brake or mechanical counterbalance. This is a safety requirement, not just a performance consideration.

Quick Selection Guide for Different Ball Screw Types

After understanding different types of ball screws, the next step is to match the type with the actual machine requirement. The table below gives a practical reference.

DLY Ball Screw Type Reference

DLY supplies rolled ball screws, ground ball screws, single nuts, double nuts, support units, and customized end machining for CNC machines, automation equipment, packaging machinery, medical equipment, and industrial motion systems.

For DLY ball screws, cold-rolled ball screws are generally C7 accuracy grade, and ground ball screws are generally C5 accuracy grade. The ball screw shaft material is S55C, and the ball nut material is 20CrMo.

When choosing the right ball screw type, diameter, lead, accuracy grade, nut structure, circulation method, preload, support units, end machining, load, speed, and installation space should be reviewed together.

Conclusion

There are many types of ball screws, and each type is designed for different machine requirements. Rolled ball screws are suitable for cost-effective general motion, while ground ball screws are used for higher precision and better lead accuracy. C7 ball screws are common in automation and general industrial equipment, while C5 ball screws are more suitable for precision CNC, inspection systems, and high-accuracy positioning axes.

Ball circulation method, nut structure, and lead size also affect the final selection. External circulation can be used for larger or heavier-load systems, internal circulation is useful for compact structures, end cap return supports smooth and high-speed movement, and double nuts help improve rigidity and backlash control when proper preload is applied.

The right ball screw type should be selected according to load, speed, accuracy, stroke, installation space, rigidity, cost, and working environment. Instead of choosing only by one parameter, it is better to review the complete motion system before confirming the final model.