Brass SEMS Screws (Washer Assembled Machine Screws)

Brass SEMS Screws – Washer Assembled Machine Screws for Electrical and Industrial Applications

Brass SEMS screws (washer assembled machine screws) are pre-assembled fasteners combining a machine screw with a captive, free-spinning washer that cannot be removed during installation or in-service. Manufactured from free-machining brass (CW614N, C36000), these screws eliminate missing-washer errors, reduce assembly time, and are widely used by electrical OEMs, EPC contractors, panel builders, and electronics manufacturers in the USA and globally. Brass SEMS screws provide consistent clamping load, corrosion resistance, and electrical conductivity in terminal blocks, switchgear, PCBs, and enclosure hardware.

Product Overview

Brass and Copper Parts manufactures brass SEMS screws to DIN 7500, DIN 912+SEMS, ASME B18.13, and customer-specific standards. The captive washer is assembled onto the screw shank during the thread rolling process, permanently trapping it between the head and thread start. This design ensures the washer is always present at the point of assembly – critical for electrical connections where a missing washer can create loose terminations, arcing, or contact failure. SEMS screws are available with plain, spring lock, or tooth lock washers in a range of head styles and drive types.

Product Types and Variants

By Head Type

• Pan Head Brass SEMS Screws – Wide low-profile head, maximum bearing area, DIN 7985 / ASME B18.6.3
• Hex Head Brass SEMS Screws – Wrench-driven hex head for higher torque applications
• Truss Head Brass SEMS Screws – Extra-wide dome head for thin sheet and soft material
• Flat Head (Countersunk) Brass SEMS Screws – Flush installation in countersunk holes
• Binding Head Brass SEMS Screws – Low cylindrical head, used in terminal blocks and wiring devices
• Cheese Head Brass SEMS Screws – Cylindrical head, DIN 84 based

By Drive Type

• Slotted Drive SEMS – Standard single slot, for manual and power tool assembly
• Phillips Drive SEMS (Pozidriv) – Cross recess type II, for automated assembly
• Combination Drive SEMS – Accepts both slotted and Phillips drivers
• Hex Socket (Allen) Drive SEMS – For high-torque installations
• Square Drive SEMS – Robertson square recess for non-slip driving

By Washer Type

• Plain Flat Washer SEMS – Distributes clamp load; prevents surface damage
• Internal Tooth Lock Washer SEMS – Provides anti-loosening under vibration; common in electrical panels
• External Tooth Lock Washer SEMS – Maximum grip on outer diameter for grounding connections
• Split (Helical Spring) Lock Washer SEMS – Traditional spring lock for vibrating assemblies
• Conical (Belleville) Washer SEMS – Maintains clamp load under thermal cycling
• Serrated Flange Washer SEMS – Integral serrations for grounding and anti-loosening

Key Features

• Captive washer – permanently assembled, cannot be lost or forgotten during installation
• Reduces assembly time and eliminates component handling errors in automated lines
• Excellent electrical conductivity – brass provides reliable grounding and bonding contact
• Corrosion-resistant copper alloy – suitable for humid, coastal, and mild chemical environments
• Non-magnetic – safe for sensitive electronics and electrical equipment
• Wide range of head styles and washer types for diverse application requirements
• Available with nickel plating for enhanced corrosion and tarnish resistance
• RoHS 2 and REACH compliant; lead-free alloy available

Technical Specifications

Raw Material Grades and International Equivalents

Applications in Industry

• Electrical OEMs and Panel Builders: Terminal block fasteners, switchgear assembly, DIN rail hardware, MCB and MCCB mounting screws
• Power Utilities and EPC Contractors: Control panel assembly, cable tray fixings, junction box hardware, substation enclosure screws
• Electronics Manufacturing: PCB mounting, chassis assembly, shielding ground connections, SMT rework hardware
• Automotive: Dashboard electronics, battery terminal connections, ECU mounting, wire harness grounding
• Telecommunications: Rack and panel hardware, antenna ground connections, server chassis assembly
• Appliance and HVAC: Sheet metal assembly, motor terminal connections, compressor assembly hardware

Manufacturing Process

Brass SEMS screws at Brass and Copper Parts are cold-headed from free-machining brass wire conforming to ASTM B16 / EN 12164. The washer is punched from brass strip and pre-loaded onto the screw shank before thread rolling. Thread rolling captures the washer permanently between the head and thread start – no welding, adhesive, or secondary operation is required. This ensures the washer spins freely and seats flat on the mating surface every time. After thread rolling, screws undergo slot milling (for slotted drives) or recess formation (for Phillips/combination drives), followed by deburring, cleaning, and plating as specified.

Quality Standards and Certifications

• ASME B18.6.3 – Machine Screws and Machine Screw Nuts
• ASME B18.13 – Screw and Washer Assemblies – SEMS (Inch Series)
• DIN 7500C – Thread Rolling Screws with Washer
• DIN 7985 – Pan Head Machine Screw with Cross Recess (Metric)
• ISO 14580 – Pan Head Screws with Hexalobular Internal Drive
• RoHS 2 Directive Compliant (including lead-free variants)
• REACH Regulation Compliant
• Material Test Certificates per EN 10204 2.1 and 3.1
• ISO 9001:2015 Quality Management System

Why Choose Brass and Copper Parts

• Complete SEMS range in-house: multiple head styles, drive types, and washer configurations
• Free-machining brass (CW614N / C36000) and lead-free alternatives for RoHS markets
• Nickel plating in-house for corrosion-resistant SEMS screws
• Proven supplier to US and European electrical OEMs and EPC contractors
• Competitive pricing with consistent dimensional quality and full traceability
• Custom packaging (bulk, bag-and-box, tape-and-reel) for automated assembly lines

Frequently Asked Questions

What does SEMS stand for?

SEMS stands for “Screw and washer aSSEMblieS” – a standardized term per ASME B18.13 for pre-assembled screw and washer combinations where the washer is captive and free-spinning on the shank.

Why use brass SEMS screws instead of separate screws and washers?

Brass SEMS screws reduce assembly time, prevent missing-washer defects, ensure consistent clamping load, and improve quality control in high-volume electrical and electronic assembly operations. They eliminate the need to handle and feed separate washers on the production line.

What washer types are available in brass SEMS?

We offer brass SEMS with plain flat, internal tooth lock, external tooth lock, split spring lock, conical Belleville, and serrated flange washers. Internal tooth lock washers are most common in electrical panel assembly for combined fastening and grounding.

Are brass SEMS screws RoHS compliant?

Yes. We supply RoHS 2-compliant brass SEMS screws in low-lead or lead-free alloy (CW614N lead-free grade or C26800). Certificate of Compliance available on request.

Can brass SEMS screws be used for electrical grounding?

Yes. Brass has 28% IACS conductivity, and SEMS screws with serrated or tooth lock washers provide a reliable, low-resistance grounding contact. They are standard hardware in electrical panel grounding assemblies.

What drive styles are available?

We manufacture brass SEMS screws with slotted, Phillips (Pozidriv), combination, hex socket (Allen), and square (Robertson) drive recesses. Combination drive is most popular for dual-tool compatibility.

What size range is available?

Inch: #2 to #12, length 1/4″ to 2″. Metric: M2 to M10, length 4mm to 50mm. Non-standard sizes and threads available for OEM programs.

Is nickel plating available on brass SEMS screws?

Yes. We offer bright nickel, electroless nickel, and tin plating options for enhanced corrosion resistance, tarnish prevention, and solderability in electronics applications.

Do you supply brass SEMS screws for automated assembly (tape and reel)?

Yes. We can supply brass SEMS screws in tape-and-reel packaging for automated vibratory bowl feed and robotic assembly systems. Specify driver diameter, tape width, and reel size when ordering.

What is the difference between DIN 7500C and ASME B18.13 SEMS?

DIN 7500C specifies thread-rolling screws with assembled washers in metric series, while ASME B18.13 covers inch-series SEMS assemblies. Both define captive washer assemblies but differ in thread, dimensional standards, and washer specifications. We can supply to either standard.

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Request a Quote

Need brass SEMS screws in specific head styles, drive types, washer configurations, or surface finishes? Brass and Copper Parts supplies precision washer-assembled machine screws to electrical OEMs, EPC contractors, panel builders, and distributors in the USA and worldwide. Contact us for samples, technical datasheets, pricing, and custom packaging options.