Date Updated:May. 07. 2025
SEMS Screws: Efficiency and Convenience in Fastening
➡Description of Special Screws for Engineers
What are SEMS screws?
SEMS screws, also known as washer-integrated screws, are screws with a pre-assembled washer on the head. This unique design eliminates the need for separate washers, streamlining the assembly process and reducing the risk of washer loss.
<General Manufacturing Process>
Benefits of using SEMS screws
Reduced assembly time and effort: no need to handle and install separate washers.
Reduced risk of (Prevent) washer loss & omission: the integrated washer is securely attached to the screw head.
Limitations of using SEMS screws
Longer incomplete thread section: the presence of the washer extends the unthreaded run‑out portion of the screw, which may not be suitable for securing thin sheets.
However, special specifications are available to address this limitation.
Please contact Customer Service for more information
Types of SEMS screws
| Designation | Washer ① | Washer ② A | Image | Description |
|---|---|---|---|---|
| P=1 | Obsolete JIS Standard Plain Washer SEMS |
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Often referred to as a Single SEMS or S SEMS, this screw features a pre-assembled obsolete JIS standard plain washer. |
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| P=2 | Spring Washer SEMS |
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This configuration, featuring a pre-assembled spring washer, is also sometimes referred to as a Single SEMS or S SEMS. |
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| P=3 | Spring Washer |
Obsolete JIS Plain Washer SEMS |
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This configuration, featuring a pre-assembled obsolete JIS plain washer and spring washer, is sometimes referred to as a Double SEMS or W SEMS. |
| P=4 | Spring Washer |
Obsolete JIS Small Plain Washer SEMS |
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This configuration, featuring a pre-assembled obsolete JIS small plain washer and spring washer, is sometimes referred to as a Double SEMS or W SEMS. |
| PK=1 | Obsolete JIS Small Plain Washer |
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This configuration, featuring a pre-assembled obsolete JIS small plain washer, is also sometimes referred to as a Single SEMS or S SEMS. |
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| I=1 | SEMS Screws with ISO Standard Plain Washers |
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This configuration, featuring a pre-assembled ISO standard plain washer, is sometimes referred to as a Single SEMS or S SEMS. |
|
| I=3 | Spring Washer |
ISO Standard Plain Washer |
 |
This configuration, featuring a pre-assembled ISO standard plain washer and spring washer, is sometimes referred to as a Double SEMS or W SEMS. |
| I=4 | Spring Washer |
ISO Standard Small Plain Washer |
 |
This configuration, featuring a pre-assembled ISO standard small plain washer and spring washer, is sometimes referred to as a Double SEMS or W SEMS. |
| IK=1 | ISO Standard Small Plain Washer SEMS |
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This configuration, featuring a pre-assembled ISO standard small plain washer, is sometimes referred to as a Single SEMS or S SEMS. |
Although multiple configurations exist, the I=1 and I=3 variants are most widely available, with NBK offering an extensive range of these standard options.
Lineup
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| Material |
SUSXM7 (Equivalent to SUS304) | SUS316L | SUS316L | SUSXM7 (Equivalent to SUS304) | SUSXM7 (Equivalent to SUS304) | SUSXM7 (Equivalent to SUS304) | SUSXM7 (Equivalent to SUS304) |
| Product Name | Hex Socket Head Cap Screws with Captive Washer and Ventilation Hole | Washer Integrated Hex Socket Head Cap Screws with Ventilation Hole - High Strength Stainless Steel | Washer Integrated Hex Socket Head Cap Screws - High Strength Stainless Steel | Hex Socket Head Cap Screws with Captive Washers（I=3） | Phillips Cross Recessed Pan Head Machine Screws with Captive Washers（I=1） | Phillips Cross Recessed Pan Head Machine Screws with Captive Washers（I=3） | Hex Socket Head Cap Screw with Captive Washer and Ventilation Hole（I=1） |
| Product Number | SVSQS | SVSQLG | SNSQLG | SNSQS | SNPI1S | SNPI3S | SVSI1S |
| Lineup |
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| Material | Grade 2 Titanium | Grade 2 Titanium | Equivalent to SUS304 | Equivalent to SUS304 |
| Product Name | Titanium Hex Socket Head Cap Screws with Captive Washers（I=1） | Titanium Hex Socket Head Cap Screws with Captive Washers（I=3） | Hexagon Head Screws with Captive Washer（P=2） | Hexagon Head Screws with Captive Washer（P=3） |
| Product Number | SNSI1T | SNSI3T | SNHP2S | SNHP3S |
| Lineup | ||||
Dimensions of Pre-assembled Washers in SEMS Screws
| Obsolete JIS Plain Washer | M3 | M4 | M5 | M6 | M8 |
|---|---|---|---|---|---|
| d（Outside Diameter） | 8 | 10 | 12 | 13 | 18 |
| t（Thickness） | 0.5 | 0.8 | 0.8 | 1.0 | 1.6 |
| Obsolete JIS small Plain Washer | M3 | M4 | M5 | M6 |
|---|---|---|---|---|
| d（Outside Diameter） | 6 | 8 | 10 | 11.5 |
| t（Thickness） | 0.5 | 0.5 | 0.8 | 0.8 |
| ISO Standard Plain Washer | M3 | M4 | M5 | M6 |
|---|---|---|---|---|
| d（Outside Diameter） | 7 | 9 | 10 | 12.5 |
| t（Thickness） | 0.5 | 0.8 | 1.0 | 1.6 |
| ISO Standard Small Plain Washer | M3 | M4 | M5 | M6 | M8 |
|---|---|---|---|---|---|
| d（Outside Diameter） | 6 | 8 | 10 | 11.5 | 15.5 |
| t（Thickness） | 0.5 | 0.8 | 1.0 | 1.6 | 1.6 |
Flange and Truss Head Screws: Optimized Bearing Surface Solutions
For applications requiring an expanded bearing surface, consider flange or truss head screws as an alternative to traditional washer configurations.
For fastening thin sheets, NBK offers custom solutions with underhead serrations, ensuring secure and reliable connections.
Related articles can be found here:
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What is a hex socket bolt?
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What is a low head screw?
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Hexagon Socket Head Cap Screws Excerpts from JIS B 1176:2015
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What is a Screw? -The Engineer's Guide-
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Special Screws Product List
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