SFE and SFU ball screws are both flange-type single-nut ball screw series, but they are designed around different lead ranges and ball-return arrangements. The most practical difference is that DLY SFE models are primarily used for large-lead, fast linear movement, while SFU models cover a broader range of standard leads for general CNC and automation axes.
The series name alone does not determine accuracy, load capacity, rigidity or service life. These values must be checked from the specific model. An SFE ball screw can be supplied in C5 or C7 accuracy, just as an SFU can be selected in different accuracy grades.
To distinguish SFE from SFU correctly, start with the model code and lead, then check the nut appearance, circulation structure and mounting drawing.
Quick Identification
| Check first | SFU ball screw | SFE ball screw |
|---|---|---|
| Model example | SFU1605, SFU2005, SFU2510 | SFE1616, SFE2525, SFE3232 |
| Lead tendency | Commonly selected with standard or moderate leads | Primarily designed around large-lead combinations |
| Nut appearance | Compact flange-type single nut | Flange nut with identifiable end-cap return sections |
| Main selection direction | General positioning, CNC and automation axes | Fast travel where a large lead is required |
Read the Model Code
The quickest way to identify the two series is to read the complete model code. The letters identify the nut series, while the following numbers normally indicate the nominal screw diameter and lead.
| Model | Nominal diameter | Lead | Travel per revolution |
|---|---|---|---|
| SFU1605 | 16 mm | 5 mm | 5 mm/rev |
| SFU1610 | 16 mm | 10 mm | 10 mm/rev |
| SFE1616 | 16 mm | 16 mm | 16 mm/rev |
| SFE2525 | 25 mm | 25 mm | 25 mm/rev |
For example, SFE2525 moves approximately 25 mm for one screw revolution, while SFU2505 moves approximately 5 mm per revolution. The SFE model therefore requires fewer revolutions to achieve the same linear travel.
Nut Structure
Both DLY SFE and SFU are flange-type single nuts, so they may look similar in a machine photo. The visible return structure is the main external clue.
The DLY SFU series uses a compact nut return arrangement according to its current product specification. The nut is commonly selected where a standard flange-type ball nut and moderate lead are required.
The DLY SFE series uses end-cap circulation. The balls are redirected through return paths at the ends of the nut, allowing the circulation system to work with the series' large-lead groove arrangement.
The material of a visible end cap should not be assumed from a photograph. Confirm the current drawing and product specification if end-cap material, temperature resistance or replacement parts are important.
Why SFE Uses a Large Lead
Linear speed is determined by screw lead and rotational speed:
If an SFU1605 and an SFE1616 both rotate at 1,000 rpm:
| Model | Lead | Screw speed | Theoretical linear speed |
|---|---|---|---|
| SFU1605 | 5 mm | 1,000 rpm | 5,000 mm/min |
| SFE1616 | 16 mm | 1,000 rpm | 16,000 mm/min |
These values show the kinematic relationship only. They are not guaranteed operating speeds. Actual permissible speed depends on screw length, root diameter, support arrangement, critical speed, ball-circulation limit, lubrication, alignment and load.
Lead Changes Motor Requirements
A larger lead gives more linear travel per revolution, but it also changes the torque and positioning relationship.
- A large lead can reach a required linear speed at lower screw rpm.
- For the same axial thrust, a larger lead generally requires more driving torque.
- One motor revolution produces a larger linear displacement.
- Encoder resolution, control resolution and positioning requirement must be checked together.
- Vertical axes require careful evaluation of back-driving and brake requirements.
Therefore, SFE should not be selected only because a machine needs to be "fast." The designer must confirm that the motor torque, acceleration, control resolution and support system are suitable for the selected lead.
Corrected SFE vs SFU Table
The original comparison table is retained below, but inaccurate absolute judgments have been replaced with model-specific selection guidance.
| Item | SFU ball screw | SFE ball screw |
|---|---|---|
| Basic structure | Compact flange-type single nut | Flange-type single nut with end-cap return sections |
| Circulation | Compact return arrangement according to the DLY SFU specification | End-cap circulation designed for the large-lead groove arrangement |
| Typical lead direction | Standard and moderate lead options | Large lead options for fast linear travel |
| Accuracy | Selected by manufacturing grade, such as C5 or C7 | Selected by manufacturing grade, such as C5 or C7 |
| Rigidity | Depends on diameter, nut design, ball circuits and preload | Depends on diameter, nut design, ball circuits and preload |
| Load capacity | Use the rated dynamic and static load of the exact model | Use the rated dynamic and static load of the exact model |
| Linear speed | Suitable for general motion; speed depends on lead and allowable rpm | Large lead provides more travel per revolution |
| Positioning resolution | Smaller leads can provide finer linear movement per motor revolution | Large lead requires the motor and feedback system to support the required resolution |
| Installation envelope | Check SFU nut diameter, flange and total length | Check SFE end-cap envelope, flange and total length |
| Typical use | CNC feed axes, automation equipment, packaging and positioning units | Fast-transfer axes, rapid positioning platforms and large-lead motion systems |
Accuracy Is Independent of Series
SFE does not mean medium accuracy, and SFU does not automatically mean high accuracy. Accuracy is primarily determined by the screw manufacturing process and specified grade.
DLY supplies C7 rolled ball screws for general industrial applications and C5 ground ball screws for equipment requiring tighter lead accuracy. The selected nut series, accuracy grade, axial clearance, end machining and support arrangement must be specified separately.
A C5 SFE ball screw may have better lead accuracy than a C7 SFU ball screw, even though the SFE uses a larger lead. Conversely, selecting C5 does not by itself guarantee zero backlash or sufficient rigidity.
Load and Rigidity Need Model Data
It is not accurate to classify all SFU ball screws as high-load and all SFE ball screws as medium-load. Load capacity changes with screw diameter, ball diameter, number of loaded circuits, nut length and contact design.
When comparing two models, check:
- Rated dynamic load
- Rated static load
- Nut rigidity or load-displacement data
- Permissible axial load
- Preload or axial-clearance specification
- Calculated service life under the actual duty cycle
The SFE2525-3 and SFE2525-6, for example, use the same nominal diameter and lead but have different circulation or loaded-circuit configurations, so their load ratings and rigidity are not identical.
Large Lead Is Not Long Stroke
Lead and stroke describe different parameters:
- Lead is the linear distance travelled during one screw revolution.
- Stroke is the total usable linear travel of the machine axis.
An SFE ball screw can provide a large lead without having a long shaft. A long-stroke ball screw can use either an SFU or SFE nut, provided that the required lead and model are available.
For a long screw shaft, critical speed, buckling, shaft deflection and support arrangement must be checked. A large lead does not remove these limitations.
For a broader explanation of large-lead selection, see the high lead ball screw guide.
Can SFE Replace SFU?
SFE and SFU should not be treated as direct replacements based only on the same screw diameter. Changing from SFU2505 to SFE2525 changes the lead from 5 mm to 25 mm, which changes travel per revolution, motor torque, acceleration, control resolution and possible back-driving behavior.
Before replacement, compare:
- Screw diameter and lead
- Ball-track geometry and shaft compatibility
- Nut outside diameter and total length
- Flange diameter, thickness and bolt-hole pattern
- Lubrication-port position
- Rated load and rigidity
- Required motor torque and maximum rpm
- Shaft-end machining and support units
A nut from one series should not be installed onto an existing screw shaft unless the ball-groove geometry, lead, ball diameter and matching requirements have been confirmed by the manufacturer.
When to Choose SFU
Start with an SFU ball screw when the application requires:
- A standard flange-type single nut
- A common diameter-and-lead combination
- General CNC or automation positioning
- A compact nut envelope
- Finer travel per motor revolution than a large-lead model
- Broad model availability for machine replacement or production use
Review the DLY SFU ball screw specifications for available diameters, leads and nut dimensions.
When to Choose SFE
Start with an SFE ball screw when the application requires:
- Large linear travel per screw revolution
- Fast positioning without excessively increasing screw rpm
- An end-cap circulation structure designed for the selected large lead
- A flange-type single nut
- A model such as SFE1616, SFE2525, SFE3232 or another available large-lead combination
Review the DLY SFE ball screw specifications for the current diameter, lead, nut and accuracy options.
Selection Sequence
A reliable SFE vs SFU decision can be made in the following order:
- Define the required linear speed. Do not begin with the series name.
- Confirm the available motor speed. Calculate the lead needed to reach the target speed.
- Calculate axial thrust and motor torque. A larger lead changes the torque requirement.
- Check positioning resolution. Include motor, encoder and control-system resolution.
- Check screw length and support method. Verify critical speed and buckling.
- Compare exact model ratings. Review dynamic load, static load and rigidity.
- Confirm the nut drawing. Check flange holes, envelope and lubrication access.
- Specify accuracy and shaft ends separately. Confirm C5 or C7 and the required BK/BF, FK/FF or EK/EF support arrangement.
Conclusion
The central difference between DLY SFE and SFU ball screws is their lead and nut-return design. SFU is a broadly used flange-type single-nut series covering common lead combinations, while SFE uses an end-cap circulation structure and is primarily designed for large-lead, fast linear movement.
SFE does not automatically mean lower accuracy, lower load or shorter life, and SFU does not automatically mean higher rigidity. These properties must be compared using the exact model, accuracy grade, load rating, preload, screw length and installation arrangement.
DLY supplies C7 rolled and C5 ground ball screws with S55C screw shafts, 20CrMo nuts and optional end machining. Provide the required speed, load, stroke, accuracy and mounting drawing when comparing SFE and SFU models.
