A "SEMS screw" is a pre-assembled unit combining a machine screw (pan, countersunk, etc.) and a washer that does not detach.
These assemblies drastically optimize efficiency on manufacturing lines by eliminating the time-consuming process of manually placing washers onto individual screws before driving them. Furthermore, they safeguard high-volume electronic assemblies against loose parts dropping into live circuits. Core Structural Classification of JIS B 1188
The standard specifies requirements for cross-recessed head screws with captive washers . These are often referred to as "Sems" screws, where a washer is permanently attached to the screw blank before the threads are rolled, preventing it from falling off. Quick Reference for JIS B 1188
| | Details | |------------|--------------| | Standard number | JIS B 1188 | | Title | Fasteners – Hexalobular socket head cap screws | | Current version (as of 2026) | JIS B 1188:2014 (confirmed) | | Corresponding international standard | ISO 14579 (modified adoption) |
For screws longer than 125mm, the minimum thread length is specified. For shorter screws, nearly full threading is required. jis b 1188 pdf
This rigorous review process ensures that JIS B 1188 remains aligned with global best practices and evolving industrial requirements. In 2021, the standard was reaffirmed, confirming its continued validity.
Used for load distribution on soft mating surfaces.
Prevents operators from forgetting to install critical locking or flat washers.
Pre-assembled parts are highly compatible with automated feed systems and robotic assembly arms. Key Technical Specifications A "SEMS screw" is a pre-assembled unit combining
The standard defines the specifications for cross-recessed head screws with captive washers , commonly known in the industry as "Sems" screws. These specialized fasteners feature pre-assembled washers that are mounted onto the screw blank before the threads are rolled, ensuring the washers remain permanently attached and free-spinning. Core Specifications of JIS B 1188
Specifically, this standard covers the dimensions, tolerances, and technical requirements for slotted (flat-blade drive) screws that are not intended for high-strength structural applications. The typical products under JIS B 1188 include:
Marine environments, medical devices, outdoor enclosures, food processing. C2700, C2600
The standard specifies various material grades depending on the intended environment: Core Structural Classification of JIS B 1188 The
In conclusion, JIS B 1188 is a widely used standard for hexagon socket head cap screws. The standard provides detailed specifications for the screws, including dimensions, materials, and testing methods. A JIS B 1188 PDF is available for download, providing access to the full text of the standard. By using JIS B 1188, manufacturers and users can ensure that screws meet the required specifications, improving quality, safety, and interchangeability.
Typically includes just a spring lock washer to resist loosening from vibration.
⚠️ : Free PDFs found on file-sharing or academic websites are likely outdated (e.g., JIS B 1188:1995) or pirated copies. Using them for commercial purposes may violate copyright laws.
JIS screws often feature slightly smaller head diameters and different head radiuses compared to their European DIN counterparts.
: Typically spans from metric sizes M2 to M10.