➡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 is sometimes called a single SEMS or S SEMS.
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.

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

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.

Flange Button Bolt

Cross Recessed Truss Head Captive Screws

Flanged Hex Socket Head Bolts

Flanged Hex Bolts

For thin sheet fastening, it is also possible to produce custom products with undercut machining beneath the head.

Related articles can be found here:

• 

  What is a hex socket bolt?

•  

  What is a low head screw?

•  

  Hexagon Socket Head Cap Screws Excerpts from JIS B 1176:2015

•  

  What is a Screw? -The Engineer's Guide-

•  

  Special Screws Product List

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