SI vs SA vs PHS vs POS Rod Ends: Thread Types and Buying Checklist
Start with the connection, not the part number
Rod end bearings connect a threaded rod or linkage to a pivoting joint. Before choosing a series, confirm whether the assembly needs an internal or external thread, the required bore diameter, the thread specification and direction, and the operating load. A matching nominal bore alone does not guarantee interchangeability.
Female and male rod ends
SI series is commonly used for female-thread rod ends, while SA series is commonly used for male-thread rod ends. PHS and POS are also widely used as female-thread and male-thread rod end designations, respectively. However, suffixes, materials, dimensions and bearing construction differ by manufacturer and standard. Always confirm the drawing and complete part number before treating two series as equivalent.
| Series | Common connection | What to verify before ordering |
|---|---|---|
| SI | Female / internal thread | Bore, thread size, thread direction, center height, housing dimensions, bearing construction |
| SA | Male / external thread | Bore, shank length, thread size, thread direction, housing dimensions, bearing construction |
| PHS | Female / internal thread | Drawing, lubrication provision, dimensions, material and load requirements |
| POS | Male / external thread | Drawing, lubrication provision, dimensions, material and load requirements |
Five checks that prevent a wrong order
- Connection: Internal or external thread, right-hand or left-hand, thread pitch and engagement length.
- Dimensions: Bearing bore, outside dimensions, ball width, center height and available mounting space.
- Load and motion: Radial and axial loads, static versus oscillating motion, impact, speed and required misalignment angle.
- Lubrication and environment: Whether periodic greasing is possible, and exposure to dust, water, corrosion or heat. Do not assume a suffix guarantees maintenance-free operation.
- Commercial details: Required quantity, tolerance or drawing, inspection requirements, packaging, and whether OEM marking is needed.
Can SI replace PHS, or SA replace POS?
Not by name alone. These families can have similar connection styles, but dimensions, bearing design, load ratings and lubrication details may differ. Cross-reference the full manufacturer drawing and application requirements before substitution.
What to send for an accurate factory quotation
Send the complete model number or a drawing, bore diameter, thread size and direction, quantity, application, and any material or packaging requirements. For a replacement, include photos and measured dimensions where available. This reduces back-and-forth and helps avoid quoting a part that fits the thread but not the joint.
Browse our product families: SI rod ends, POS/POSL rod ends, and bearing product catalog. For a model-specific quotation, use our contact page.