A4 Stainless Steel SEMS Screws with Captive Flat Washers are supplied to ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80. Corrosion behaviour is superior, including marine and chloride environments, the material is largely non-magnetic, and the usable service range is approx. -200 °C to +400 °C, subject to the property class and the joint. In practice this grade is specified for marine, coastal and chemical applications.
- Grade
- ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80
- Corrosion resistance
- Superior, including marine and chloride environments
- Magnetic response
- Largely non-magnetic
- Service temperature
- approx. -200 °C to +400 °C, subject to the property class and the joint
Property values are typical for the grade. Certified mechanical test data is available on request for production orders.
Material specification page for sems screws with captive flat washers in A4 Stainless Steel. Covers the grade designation (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80), corrosion and magnetic behavior, comparable grades and their trade-offs, and the sizes available to DIN 7985 / ISO 7045 and EN ISO 10644.
Why Choose A4 Stainless Steel for SEMS Screws with Captive Flat Washers
Specified for marine, coastal and chemical applications. For sems screws with captive flat washers, this matters when superior, including marine and chloride environments is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80 |
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| Magnetic response | Largely non-magnetic |
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| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
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| Corrosion characteristic | Superior, including marine and chloride environments |
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Corrosion Behavior in Service
A4 (316) adds 2–3% molybdenum to the A2 (304) composition, which dramatically improves resistance to chloride-pitting corrosion. For SEMS Screws with Captive Flat Washers in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Comparable Grades
For SEMS Screws with Captive Flat Washers, the alternative stainless grade is A2 (304). A2 (304) suits general indoor and outdoor service; A4 (316) adds molybdenum for marine and chloride environments. Where higher strength matters more than corrosion, switch to plated alloy-steel class 8.8 or 10.9.
Using Stainless Fasteners in Aluminum
Stainless steel is more noble than aluminum, so in the presence of an electrolyte — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. The effect is driven by the area ratio: a small stainless fastener in a large aluminum section is normally acceptable, while a large stainless fastener in thin aluminum is not. Where the joint is wet, isolate the two metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.
Sizes of SEMS Screws with Captive Flat Washers Available in A4 Stainless Steel
| Thread size | Pitch (mm) | Washer outside diameter (mm) | Washer thickness (mm) | Property/material options | Drive | Reference standard |
|---|
| M2.5 | 0.45 | 6 | 0.6 | steel 4.8/8.8 or A2 stainless | Phillips | DIN 7985 / ISO 7045 and EN ISO 10644 |
| M3 | 0.5 | 7 | 0.6 | steel 4.8/8.8 or A2 stainless | Phillips | DIN 7985 / ISO 7045 and EN ISO 10644 |
| M4 | 0.7 | 9 | 0.8 | steel 4.8/8.8 or A2 stainless | Phillips | DIN 7985 / ISO 7045 and EN ISO 10644 |
| M5 | 0.8 | 10 | 1.0 | steel 4.8/8.8 or A2 stainless | Phillips | DIN 7985 / ISO 7045 and EN ISO 10644 |
| M6 | 1.0 | 12 | 1.6 | steel 4.8/8.8 or A2 stainless | Phillips | DIN 7985 / ISO 7045 and EN ISO 10644 |
| M8 | 1.25 | 16 | 2.0 | steel 4.8/8.8 or A2 stainless | Phillips | DIN 7985 / ISO 7045 and EN ISO 10644 |
Applications & Industries
Where SEMS Screws with Captive Flat Washers are used, and what decides the specification in each case. Stocked from M2.5 to M8.
Industries that specify SEMS Screws with Captive Flat Washers
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Electrical assembly
Captive flat-washer screws for panels, terminals and equipment covers.
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Appliance production
High-volume screwdriving where a separate washer would slow assembly.
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Sheet-metal enclosures
Removable covers that must retain the washer on the screw.
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Machine guarding
Service hardware that stays with the cover during removal.
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Steel fabrication
Bolted connections in frames, enclosures, walkways and weldments, on the bench and on site.
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Energy & infrastructure
Tower, pipework, switchgear and plant fixings specified for long service life and inspectable joints.
Typical applications
- combining the screw and flat washer into one captive assembly
- spreading bearing load while preventing washer loss during service
- using a Phillips drive for controlled production installation
- selecting the washer outside diameter and thickness with the thread size
- clamping two machined faces to a calculated preload
- bolting brackets, motors and gearboxes to a frame
Service conditions to specify against
- Marine and coastal
- Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
- High load
- Supplied in ISO 898-1 property classes, so the joint can be designed to a stated proof load and tightened to a calculated torque rather than by feel.
- Torque and preload
- The joint is designed around bolt tension, so lubrication, coating and the friction coefficient all change the torque figure — state them together.
Where to use something else
- Do not substitute the captive washer for a hardened structural washer in a high-preload joint.
- Do not use a machine thread into unthreaded sheet or timber; use a tapping screw, rivet nut or insert made for that parent material.
Full application guide: where SEMS Screws with Captive Flat Washers are used, how to specify them, and the cases they are wrong for
