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When a linkage joint needs to handle misalignment, vibration, or multi-axis movement without binding, a poorly chosen bearing becomes the weakest point in the entire assembly. Engineers, robotics builders, and machine designers working on steering systems, suspension linkages, CNC actuators, and industrial automation rely on SI female series rod end bearings to deliver consistent, low-friction articulation under load.
These SI female rod end bearings feature a steel body with an internal (female) threaded shank and a chromium steel spherical ball insert. The female thread allows the bearing to thread directly onto a male-threaded rod or stud, simplifying assembly. Available in bore sizes from M3 (3 mm / 0.12 in) through M30 (30 mm / 1.18 in), with both right-hand and left-hand thread options, and sold individually or in pairs.
Typical applications include push-pull rod linkages in automotive steering and suspension, servo and actuator end connections in robotics and CNC machines, agricultural equipment control rods, and industrial machinery pivot joints requiring angular misalignment compensation of typically 8°–12°.
The SI-series shank is internally threaded, allowing direct installation onto any compatible male-threaded rod or stud — no additional hardware required for basic assembly.
Covers 15 metric thread sizes from M3 through M30, making these SI female rod end bearings suitable for light-duty robotics linkages up to heavy industrial control rods.
Both thread directions are available for every size. Pairing a right-hand and left-hand rod end on a single rod creates a turnbuckle effect for precise length adjustment without disassembly.
The chromium steel spherical ball insert accommodates angular misalignment (typically 8°–12°), absorbing vibration and preventing binding in dynamic linkage applications.
The steel body and ball provide structural rigidity for load-bearing joints. The surface finish (zinc plating or equivalent) offers protection against light moisture and oxidation in typical indoor and sheltered environments.
Order a single bearing for a replacement or prototype, or select the 2-piece option for paired linkage assemblies — both options are available for every size and thread direction.
| Series | SI (Female Thread) |
|---|---|
| Thread Type | Female (Internal) Thread |
| Thread Direction | Right-Hand or Left-Hand (see variant options) |
| Thread Size Range | M3 to M30 |
| Body Material | Steel |
| Ball Material | Chromium Steel |
| Surface Finish | See variant options |
| Angular Misalignment | Typically 8°–12° |
| Bore Diameter Range | 3 mm – 30 mm (0.12 in – 1.18 in) |
| Quantity per Order | 1 Pcs or 2 Pcs (see variant options) |
| Standard | DIN ISO 12240-4 (SI series) |
The SI series has a female (internal) threaded shank — the bearing threads onto a male rod or stud. The SA series has a male (external) threaded shank — it threads into a female-threaded clevis or housing. For a turnbuckle-style adjustable linkage, you pair one SI (female) and one SA (male) rod end on opposite ends of a threaded rod.
Match the thread size to the male-threaded rod or stud you are connecting to. For example, if your rod is M10 with a 1.5 mm pitch, select the SI 10T/K variant. As a general guide, M3–M6 suits light-duty robotics and servo linkages; M8–M16 covers mid-range CNC actuators and automotive tie rods; M18–M30 is appropriate for heavy industrial control rods and agricultural equipment.
Use a left-hand thread rod end on one end of a threaded rod when you want to create a turnbuckle assembly. Rotating the rod will simultaneously tighten one end and loosen the other, allowing precise length adjustment without removing either rod end. If you only need a single fixed connection, a right-hand thread is the standard choice.
Load capacity varies by size — larger thread sizes carry significantly higher radial and axial loads. Specific dynamic and static load ratings depend on the exact variant; please contact us to confirm load ratings for your size if you are working to a specific engineering specification. As a conservative guide, M3–M6 sizes are suited to light loads (typically under 1 kN radial), while M20–M30 sizes handle substantially higher loads.
The steel body and ball provide good structural strength, and the surface finish offers protection against light moisture in sheltered or indoor environments. For prolonged outdoor exposure, high humidity, or contact with chemicals, consider applying additional corrosion protection (grease, sealant, or protective coating) or contact us to discuss material options for your specific environment.
SI-series rod end bearings are designed for oscillating and articulating motion — angular misalignment compensation in linkages, not continuous rotation. For continuous shaft rotation, a standard radial ball bearing is more appropriate. These rod ends are ideal for push-pull rods, steering linkages, actuator connections, and pivot joints where the motion is angular or reciprocating.
For standard steel/steel SI rod ends, periodic lubrication with a suitable grease (lithium-based or equivalent) is recommended to maintain smooth articulation and extend service life, especially in high-cycle or load-bearing applications. Some variants may include a lubrication port; check your specific size. Light-duty or low-cycle applications may operate satisfactorily with initial factory lubrication for extended periods.
