The SFI ball screw is an internally recirculating ball screw series with a flanged single nut. Its flange geometry and mounting-hole arrangement differ from the common SFU nut form, giving designers another installation option when matching an existing nut seat or planning a new linear transmission assembly.
DLY SFI models cover nominal screw diameters from 16 mm to 80 mm. Available leads include 4 mm, 5 mm and 10 mm, depending on the selected diameter. C7 rolled ball screws are the standard configuration, while C5 ground accuracy can be confirmed for applications requiring greater positioning accuracy.
SFI Nut Structure
SFI uses an internal ball recirculation system and a single flanged nut. Because the return path is contained within the nut body, there is no external return tube projecting from the nut.
The SFI flange profile and mounting-hole layout are important selection dimensions. An SFI nut should therefore not be selected only by screw diameter and lead, especially when it is intended to replace a nut already installed in a machine.
SFI Ball Screw Specifications
| Model | Diameter d (mm) |
Lead l (mm) |
Ball Diameter Da (mm) |
Nut Length L (mm) |
Circuits N |
Dynamic Load Ca (kgf) |
Static Load Coa (kgf) |
Stiffness K (kgf/μm) |
|---|---|---|---|---|---|---|---|---|
| SFI1604-4 ★ | 16 | 4 | 2.381 | 45 | 4 | 640 | 1,340 | 16 |
| SFI1605-3 ★ | 16 | 5 | 3.175 | 43 | 3 | 765 | 1,240 | 17 |
| SFI1605-4 ★ | 16 | 5 | 3.175 | 50 | 4 | 780 | 1,790 | 20 |
| SFI1610-3/2 ★ | 16 | 10 | 3.175 | 47 | 3 | 833 | 1,249 | 15 |
| SFI2005-3 ★ | 20 | 5 | 3.175 | 43 | 3 | 860 | 1,710 | 22 |
| SFI2005-4 | 20 | 5 | 3.175 | 51 | 4 | 1,130 | 2,380 | 25 |
| SFI2010-3/2 ★ | 20 | 10 | 3.175 | 47 | 3 | 830 | 1,680 | 20 |
| SFI2505-3 | 25 | 5 | 3.175 | 43 | 3 | 980 | 2,300 | 26 |
| SFI2505-4 | 25 | 5 | 3.175 | 51 | 4 | 1,280 | 3,110 | 35 |
| SFI2510-4/2 ★ | 25 | 10 | 3.175 | 54 | 4 | 1,150 | 2,950 | 30 |
| SFI2510-4 ★ | 25 | 10 | 4.762 | 85 | 4 | 1,944 | 3,877 | 33 |
| SFI3205-4 | 32 | 5 | 3.175 | 52 | 4 | 1,450 | 4,150 | 40 |
| SFI3210-4 ★ | 32 | 10 | 6.35 | 90 | 4 | 3,390 | 7,170 | 45 |
| SFI4005-4 ★ | 40 | 5 | 3.175 | 55 | 4 | 1,610 | 5,330 | 49 |
| SFI4010-4 ★ | 40 | 10 | 6.35 | 93 | 4 | 3,910 | 9,520 | 50 |
| SFI5005-4 ★ | 50 | 5 | 3.175 | 55 | 4 | 1,730 | 6,760 | 60 |
| SFI5010-4 ★ | 50 | 10 | 6.35 | 93 | 4 | 4,450 | 12,500 | 65 |
| SFI6310-4 ★ | 63 | 10 | 6.35 | 98 | 4 | 5,070 | 16,600 | 80 |
| SFI8010-4 ★ | 80 | 10 | 6.35 | 98 | 4 | 5,620 | 21,300 | 90 |
| SFI8010-4 | 80 | 10 | 6.35 | 107 | 4 | 5,620 | 21,300 | 90 |
| SFI8010-6 | 80 | 10 | 6.35 | 220 | 6 | 7,810 | 31,800 | 106 |
★ Models marked with a star use a made-to-order nut configuration. Dimensions are in millimetres. Ca and Coa are stated in kgf; stiffness K is stated in kgf/μm.
Understanding the Model Number
The first four digits indicate the nominal screw diameter and lead. For example, SFI2005 has a 20 mm nominal diameter and a 5 mm lead. The suffix identifies the number or arrangement of ball circuits.
Models with the same diameter and lead can have different nut lengths, circuit arrangements and load ratings. For example, SFI1605-3 and SFI1605-4 are both 16 × 5 mm ball screws, but the four-circuit version has a longer nut and a higher static load rating.
SFI and SFU Nut Forms
SFI and SFU can share common diameter-and-lead combinations, but their nut bodies, flange profiles and mounting dimensions are not automatically interchangeable. When replacing an existing ball screw, compare the nut outside diameter, flange size, nut length and mounting-hole positions with the original drawing.
For applications that require the more commonly used external-circulation nut form, view the SFU ball screw.
Accuracy and Materials
- Standard accuracy: C7 rolled ball screw.
- Optional accuracy: C5 ground ball screw, subject to model confirmation.
- Screw shaft material: S55C.
- Ball nut material: 20CrMo.
- Nut structure: Internally recirculating flanged single nut.
- Thread direction: Right-hand thread is standard.
Selecting an SFI Ball Screw
Selection should begin with the required screw diameter and lead, followed by the nut mounting dimensions. Dynamic load rating, static load rating and stiffness should then be checked against the actual axial load, speed, stroke, duty cycle and required service life.
To confirm the correct configuration, provide the complete SFI model, total screw length, accuracy grade, shaft-end drawing, operating load and required quantity.
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