| Property class | Tensile strength (MPa) | Hardness (HRC) | |----------------|------------------------|----------------| | 8.8 | 800 min | 22–32 | | 10.9 | 1040 min | 32–39 | | 12.9 | 1220 min | 39–44 |
If "JIS B 1188" refers to something specific not covered here, please adjust according to the actual content and purpose of the standard.
JIS B 1188 is the Japanese Industrial Standard for cross-recessed head screws with captive washers, commonly known as SEMS screws. These fasteners are pre-assembled with one or two washers before the threads are rolled, ensuring the washers remain permanently attached to the screw. Technical Overview
Design: Typically features a Phillips pan head screw paired with a helical split lock washer and a flat washer. jis b 1188 pdf
Materials: Available in carbon steel (Class 4.8) or stainless steel (A2/18-8).
Common Applications: Widely used in the electronics industry due to their efficiency in assembly and economic advantage over specialized conical washer screws.
Current Version: The latest standard is JIS B 1188:2017, which superseded the 1995 version. Key Specifications (Example M4 Dimensions) | Property class | Tensile strength (MPa) |
According to typical JIS B 1188 data sheets, the dimensions for a standard M4 screw include: Thread Diameter: 4 mm Head Diameter (dk): 7 mm Head Height (k): 2.6 mm
Washer Outer Diameter: Generally 8 mm to 10 mm depending on the specific assembly type. Procurement and Downloads
Full PDF versions of the official standard can be purchased from authorized distributors: For a one-off inspection, you can rent the
Japanese Standards Association (JSA): The original publisher through their official portal.
ANSI Webstore: Provides electronic Adobe Acrobat PDF versions.
Accuris Standards Store: Offers the current 2017 revision with detailed scope and normative references. JIS B1188 Double Washer Sems
For a one-off inspection, you can rent the PDF for 24 hours at about 30% of the purchase price. Download, take notes, and it self-destructs.