Industry knowledge
Washer Retention Is the Key Value of SEMS Assembly
SEMS Screws are designed so the washer is assembled before thread rolling and then retained after the thread is formed. This prevents the washer from falling off during packaging, transportation, feeding, and assembly, which is especially useful for production lines that require fast and repeatable fastening.
For buyers, the main benefit is not only reducing missing washer problems. It also simplifies material preparation and reduces manual handling during installation. A retained washer can improve assembly efficiency and reduce the risk of incorrect washer matching.
Practical points to confirm before production
- Washer type, such as flat washer, spring washer, toothed washer, or spline washer.
- Washer inner diameter, outer diameter, thickness, hardness, and surface treatment.
- Whether the washer must rotate freely or only remain captive on the screw.
- Thread rolling allowance so the washer is retained without damaging screw function.
- Compatibility with automatic feeding equipment and assembly tools.
At Anzhikou, we usually review the screw, washer, and assembly process together, because washer retention quality depends on the full combination structure rather than one single dimension.
Choosing Double or Triple Combination Structures
Combination Screws can be designed as double combination or triple combination types depending on the application. A double combination screw usually includes one screw and one washer, while a triple combination screw may include a screw, a flat washer, and a spring washer or another functional washer. The correct choice depends on clamping area, vibration resistance, surface protection, and assembly speed.
Selection reference for common combination screw structures
| Combination Type |
Typical Structure |
Buyer Attention Point |
| Double combination |
Screw with one washer |
Suitable when load distribution or surface protection is the main need |
| Triple combination |
Screw with flat washer and spring washer |
Useful when clamping support and anti-loosening effect are both required |
| Special washer combination |
Screw with toothed, spline, wave, or customized washer |
Washer function should match the mating surface and torque requirement |
With more than 200 sets of precision equipment for cold heading, thread rolling, CNC processing, and anti-loosing treatment, Anzhikou can support different combination structures for electrical, machinery, furniture, and customized assembly applications.
Material and Surface Treatment Decisions for Combination SEMS Screws
Combination SEMS Screws are commonly made from carbon steel or stainless steel, but the correct material depends on strength, corrosion resistance, appearance, conductivity, and cost requirements. Carbon steel combination screws usually need electroplating to reduce rust risk, while stainless steel screws may be used directly or treated with polishing, passivation, or other surface finishing.
Buyers should also remember that the screw and washer may have different material behavior. Coating thickness, washer hardness, spring washer elasticity, and thread fit can all affect final assembly performance. Surface treatment should be selected for the complete screw-and-washer set, not only for the screw body.
Material and finish checks
- Confirm whether carbon steel requires zinc plating, nickel plating, black finish, or another anti-rust treatment.
- Check whether stainless steel needs passivation, polishing, cleaning, or direct natural finish.
- Confirm whether the washer material and screw material must be the same.
- Evaluate whether plating thickness affects washer movement or thread engagement.
- Define corrosion resistance, appearance consistency, and packaging protection requirements.
Anzhikou has complete testing equipment and ISO9001:2015 quality system certification, so we can help buyers set practical inspection standards for dimensions, surface finish, and combination fit.
Inspection Focus for Washer Movement, Torque, and Batch Stability
Combination SEMS screws inspection should include the screw, the washer, and the assembled relationship between them. A screw may meet thread dimensions, but the product can still fail if the washer is too tight, too loose, cracked, missing elasticity, or damaged during thread rolling.
For production-line use, consistency is especially important because combination screws are often selected to improve speed and reduce assembly steps. Stable washer retention and smooth tool engagement are key indicators of reliable batch production.
Recommended inspection items
- Thread size, total length, head diameter, head height, and drive depth.
- Washer outer diameter, inner diameter, thickness, hardness, and surface finish.
- Washer retention after thread rolling and whether the washer can fall off during handling.
- Washer rotation or movement requirements according to the application.
- Tightening torque, anti-loosening performance, burr control, and packaging protection.
With 20 years of non-standard screw customization experience, Anzhikou can support customized SEMS and combination screw orders that require stable washer assembly, practical inspection control, and efficient mass production.
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