S-Type DIN912 Double Washer Socket Cap Head SEMS Screws – High Tensile Stainless Steel (A2-70)

FULLERKREG S-Type Double Washer Socket Cap Head SEMS Screws combine an ISO 4762 hex socket cap head screw with two captive washers — a standard flat washer and a lock washer — permanently assembled onto the shank by thread rolling. Available in 304 A2-70 stainless steel, these screws eliminate loose washer handling, reduce assembly errors, and improve fastening reliability in demanding industrial environments.

Din912 + Flat + Lock Washer

What are Socket Cap Head SEMS Screws?

SEMS (pre-assembled screw and washer) screws are integrated fasteners that combine a socket cap head screw with one or more captive washers — typically a flat washer, a spring/lock washer, or both — into a single unit. The washers are permanently retained on the screw shank during manufacturing via a thread-rolling process, ensuring they cannot fall off during handling or installation.

The S-Type Double Washer configuration features both a standard flat washer (STD) and a lock washer captivated together. The hex socket (Allen key) drive head conforms to ISO 4762, providing high torque capacity and compatibility with standard tooling. This design is especially beneficial in precision manufacturing, electronics assembly, automotive production, and any application where component control and assembly speed are critical.

How the captive washer works: During production, the washers are threaded onto the screw blank before the threads are rolled. The rolled threads create a shoulder that retains the washers permanently — they can rotate freely but cannot be removed. This ensures the washer is always present and correctly positioned at the point of fastening.

Benefits of Using SEMS Screws

• Eliminates loose washers — washers are captivated and cannot be lost during handling, kitting, or installation, reducing assembly errors and line stoppages.
• Faster assembly — operators handle one integrated component instead of three separate parts (screw + flat washer + lock washer), significantly reducing cycle time.
• Consistent washer positioning — the washer is always correctly seated under the head, ensuring uniform clamping load and preventing misalignment.
• Improved vibration resistance — the integrated lock washer provides reliable anti-loosening performance without additional components.
• Reduced inventory complexity — one SKU replaces three separate part numbers, simplifying procurement, storage, and BOM management.
• Automation-friendly — the single-piece design is compatible with automated feeding and driving equipment, supporting high-volume production lines.
• Corrosion resistance — A2-70 (SUS304) stainless steel with passivated finish provides excellent resistance to oxidation, moisture, and mild chemical environments.
• RoHS and REACH compliant — all finishes meet environmental compliance requirements for global markets.

Limitations of Using SEMS Screws

• Fixed washer configuration — the washer type and size are determined at manufacture; they cannot be changed or substituted in the field.
• Higher unit cost — SEMS screws carry a premium over equivalent loose-component assemblies due to the additional manufacturing step.
• Minimum plate thickness requirement — the captive washer assembly adds a minimum stack height; very thin sheet metal applications may require careful selection of screw length.
• Not suitable for all joint configurations — applications requiring oversized, specialty, or non-standard washers must use separate components.
• Washer cannot be removed for inspection — the captive design means the washer condition cannot be independently inspected or replaced without replacing the entire fastener.

Material / Finish

All finishes are RoHS and REACH compliant.

Dimensions of Pre-Assembled Washers in SEMS Screws

The S-Type configuration uses Standard (STD) flat washers conforming to ISO standard dimensions. The following table shows the outer diameter (d) and thickness (t) of the captive flat washers by thread size:

ISO Standard Plain Washer (STD – used in S-Type)

Dimensional Data – Metric Series (ISO 4762 Head, A2-70)

All dimensions in mm. Head dimensions conform to ISO 4762. Thread rolled to BS 3643, Class 6g.

① Distance before full thread starts.   ② Washers in compressed state.   All dimensions in mm.
Unit Weight (g): to be updated. Contact FULLERKREG for weight data sheets.

Available Lengths (L ±0.5 mm): 6 mm · 8 mm · 10 mm · 12 mm · 16 mm · 20 mm · 25 mm · 30 mm

Product Showcase

Application

FULLERKREG S-Type Double Washer Socket Cap Head SEMS Screws are engineered for applications where reliable fastening, vibration resistance, and assembly efficiency are essential:

• Electronics & Semiconductor Equipment – PCB mounting, enclosure assembly, precision instrument panels where loose washers pose contamination risks.
• Automotive & Transportation – Body panel fastening, interior trim, underbody components subject to vibration and thermal cycling.
• Industrial Machinery – General machine assembly, conveyor systems, pump and motor housings requiring secure, repeatable fastening.
• Offshore & Marine – Corrosion-resistant A2-70 stainless steel makes these screws suitable for saltwater-exposed structures and offshore instruments.
• Sheet Metal Fabrication – Exterior panels, enclosures, and structural sheet metal where the captive washer distributes load and prevents pull-through.
• Cleanroom & Medical Devices – Available with Cleanroom Wash & Packaging Service; eliminates particle generation from loose washer handling.
• Renewable Energy – Solar panel mounting frames, wind turbine nacelle components, and electrical cabinet assembly.

Why FULLERKREG?

• 🏭 Direct Manufacturer – Domestic production capability with full quality control from raw material to finished fastener.
• 📐 Engineering-Grade Data – Complete dimensional data, material certifications, and test reports available on request.
• 📦 Bulk & Wholesale Supply – Competitive pricing for high-volume orders; custom packaging and kitting available.
• 🌍 Global Distribution – Experienced in international logistics and export documentation for worldwide customers.
• ✅ Compliance – RoHS and REACH compliant; ISO-standard dimensions; material traceability available.
• 🔧 Custom Specifications – Special dimensions, lengths, finishes, and patch lock options available on request.
• 🧪 Related Services – Cleanroom Wash & Packaging Service and Vibration Resistant Treatment Service available.