Date Published:Oct. 08. 2024 Date Updated:Nov. 26. 2024
What are Washer-Integrated Screws (SEMS Screws)?An Explanation of Standards and Features
➡Description of Special Screws for Engineers
What are Washer-Integrated Screws (SEMS Screws)?
A washer-integrated screw, as the name suggests, is a screw with a pre-assembled washer.
It is also commonly referred to as a SEMS screw.
In JIS standards, it is known as "Washer-integrated cross recessed head screws (JIS B1188)" and "Washer-integrated hexagon bolts (JIS B1187)."
As shown in the diagram below, the washer is assembled onto the blank material before the thread is formed, and then the threads are rolled.
Due to this manufacturing process, the thread diameter becomes larger than the inner diameter of the washer, so the washer will not come off the screw.
<General Manufacturing Process>
Advantages
Since the washer is pre-assembled, the effort of attaching the washer during assembly work can be reduced.
Additionally, there is no concern about forgetting to attach the washer or it falling off.
Disadvantages
Since the incomplete thread section (the dimension from the bearing surface to the fully threaded part) is longer than that of standard screws, it is not suitable for securing thin sheets.
Bolts for fixing thin plates are also available with special specifications such as dimensions, material, head shape, and so on.
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Types of washer-integrated screws (SEMS screws)
Designation | Washer ① | Washer ②A | Image | Description |
---|---|---|---|---|
P=1 |
Old JIS plain washer |
A screw with one old JIS plain washer assembled |
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P=2 | Spring washer | A screw with one spring washer assembled is also sometimes called a single SEMS or S SEMS. |
||
P=3 | Spring washer |
Old JIS plain washer |
A screw with one old JIS plain washer and one spring washer assembled is sometimes called a double SEMS or W SEMS. |
|
P=4 | Spring washer |
Old JIS small plain washer |
A screw with one old JIS small plain washer and one spring washer assembled is sometimes called a double SEMS or W SEMS. |
|
PK=1 |
Old JIS small plain washer |
A screw with one old JIS small plain washer assembled is also sometimes called a single SEMS or S SEMS. |
||
I=1 |
ISO plain washer |
A screw with one ISO plain washer assembled is sometimes called a single SEMS or S SEMS. |
||
I=3 | Spring washer |
ISO plain washer |
A screw with one ISO plain washer and one spring washer assembled is sometimes called a double SEMS or W SEMS. |
|
I=4 | Spring washer |
ISO small plain washer |
A screw with one ISO small plain washer and one spring washer assembled is sometimes called a double SEMS or W SEMS. |
|
IK=1 | ISO small plain washer |
A screw with one ISO small plain washer assembled is sometimes called a single SEMS or S SEMS. |
There are many standards, but I=1 or I=3 are more readily available, and NBK offers a wide lineup of these.
Lineup
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 |
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 |
Flat Washer Dimensions for Integrated Washer Screws
Old 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 |
Old 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 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 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 |
Introduction to Flange and Truss Head Screws
If the goal is to increase the bearing surface, it is recommended to use flange-shaped screws or truss-shaped screws instead of using washers.
For thin sheet fastening, it is also possible to produce custom products with undercut machining beneath the head.
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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