AISI 304 (A2) Stainless Steel / EPDM Sealing Washers — Whitened & Passivated

FULLERKREG A2 stainless steel / EPDM sealing washers consist of an A2 stainless steel (AISI 304 / SUS304 / 1.4301) metal ring with a vulcanized EPDM (ethylene-propylene-diene rubber) sealing layer bonded to the underside. The EPDM gasket is permanently bonded to the stainless steel backing — it cannot be displaced during installation. These sealing washers are used wherever water must not penetrate through fastening holes: roofing, facade cladding, trapezoidal sheet metal connections, and general weatherproof bolted joints. The stainless steel backing improves the dynamic strength of the connection and distributes the clamping load, while the EPDM gasket provides a reliable, long-lasting weatherproof seal. Compatible with commercially available screws for facade connections and trapezoidal sheet metal.

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Product Highlights

• Construction: A2 stainless steel ring + EPDM gasket, vulcanized and permanently bonded
• Metal material: A2 / AISI 304 / SUS304 / 1.4301 (austenitic stainless steel)
• Surface treatment: Whitened & passivated
• Gasket material: EPDM (ethylene-propylene-diene rubber) — Shore A 60±5
• Product class: A
• Size range: M4 – M12 (metric) / #10 – 1" (imperial)
• Waterproof sealing: Prevents water ingress through fastening holes
• EPDM properties: UV resistant, ozone resistant, weatherproof, -40°C to +120°C
• Non-magnetic, corrosion-resistant stainless steel backing
• RoHS & REACH Compliant

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Dimensional Specifications — A2 Stainless Steel / EPDM Sealing Washer

All dimensions in millimeters (mm). S = steel OD; N = steel ID; G = steel thickness; C = EPDM ID; E = EPDM thickness.

For Thread	S OD max	S OD min	N ID max	N ID min	G (steel) ref	C (EPDM ID) max	C (EPDM ID) min	E (EPDM) max	E (EPDM) min
M5 (#10)	14.2	12.5	5.6	5.3	0.8	3.9	3.7	2.2	1.8
M6 (1/4")	16.0	14.1	6.6	6.2	0.8	4.2	3.8	2.2	1.8
M8 (5/16")	19.1	18.8	8.6	8.2	0.8	5.8	5.4	2.2	1.8
M8 (3/8")	19.1	18.8	10.7	10.2	0.8	9.1	8.5	2.2	1.8
M10 (7/16")	25.5	25.0	12.4	11.9	0.8	9.8	9.2	2.2	1.8
M12 (1/2")	25.5	25.0	13.2	12.7	0.8	12.3	11.6	2.2	1.8
M20 (3/4")	38.2	37.9	21.3	20.7	0.8	19.6	18.9	2.2	1.8
M25 (1")	50.9	50.5	26.3	25.7	0.8	26.2	25.7	2.2	1.8

S = outside diameter of steel section; N = inside diameter of steel section; G = thickness of steel section; C = inside diameter of EPDM section; E = thickness of EPDM section. All dimensions in mm.

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Material Properties

Metal Section — A2 Stainless Steel (SUS304)

Property	Value
Material Grade	A2 / AISI 304 / SUS304 / 1.4301
Cr Content	17.5 – 19.5%
Ni Content	8.0 – 10.5%
Surface Treatment	Whitened & Passivated
Magnetic	Non-magnetic (austenitic)
Corrosion Resistance	Excellent — atmospheric, fresh water, mild chemicals
Product Class	A

Gasket Section — EPDM Rubber

Property	Value
Material	EPDM (Ethylene-Propylene-Diene Rubber)
Hardness	Shore A 60 ± 5
Temperature Range	-40°C to +120°C
UV Resistance	Excellent
Ozone Resistance	Excellent
Weather Resistance	Excellent — long-term outdoor durability
Water Resistance	Excellent — waterproof sealing
Bonding	Vulcanized — permanently bonded to steel, cannot be displaced

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How EPDM Sealing Washers Work

• Dual function: The stainless steel ring distributes clamping load and improves connection strength; the EPDM gasket provides a waterproof seal around the fastening hole
• Permanent bond: EPDM is vulcanized directly to the stainless steel — the gasket cannot shift or be displaced during screw driving or under service loads
• Compression sealing: When the screw is tightened, the EPDM compresses against the substrate surface, forming a continuous waterproof seal around the hole
• Self-centering: The EPDM inner diameter is smaller than the steel inner diameter — the screw passes through the EPDM, which seals against the screw shank
• Long-term durability: EPDM maintains elasticity and sealing performance over decades of outdoor UV and weather exposure

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Application Scenarios

• Roofing & roof cladding — waterproof fastening of metal roof panels, preventing water ingress at screw holes
• Facade & wall cladding — facade screw connections requiring weatherproof sealing
• Trapezoidal sheet metal — compatible with standard facade and trapezoidal sheet screws
• Skylights & glazing systems — weatherproof fastening of transparent and translucent panels
• Solar panel mounting — waterproof fastening in outdoor photovoltaic installations
• General weatherproof bolted joints — wherever water must not penetrate through fastening holes
• Marine & coastal structures — A2 stainless steel for salt air environments

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Product Photo Gallery

FULLERKREG A2 Stainless Steel / EPDM Sealing Washers:

[ Photo 1 ]

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Why Choose FULLERKREG?

• 🏭 Direct manufacturer — factory in China, no middlemen
• 📐 Strict dimensional control — 100% inspection on steel OD/ID and EPDM bonding quality
• 🌍 Global export experience — serving distributors in Europe, North America, Southeast Asia
• 📦 Flexible MOQ — small trial orders and large bulk shipments both welcome
• 📋 Full documentation — material certs, EPDM data sheets, RoHS declarations available
• ⚡ Fast lead times — standard sizes in stock, ready to ship

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Frequently Asked Questions

Q: What is an EPDM sealing washer?
A: An EPDM sealing washer (also called a bonded sealing washer or sealing washer) consists of a metal ring with an EPDM rubber gasket vulcanized to the underside. When tightened, the EPDM compresses against the substrate to form a waterproof seal around the fastening hole, preventing water ingress.

Q: Why use A2 stainless steel for the metal backing?
A: A2 (SUS304) provides excellent corrosion resistance for outdoor and coastal applications, is non-magnetic, and maintains its appearance over decades of weather exposure. It is the standard choice for roofing and facade applications where long-term durability is required.

Q: What is EPDM and why is it used for sealing washers?
A: EPDM (ethylene-propylene-diene rubber) has excellent UV, ozone, and weather resistance, maintaining elasticity from -40°C to +120°C. It provides long-term waterproof sealing performance in outdoor applications — far superior to natural rubber or neoprene for UV-exposed applications.

Q: Can the EPDM gasket be displaced during installation?
A: No. The EPDM is vulcanized (permanently bonded) to the stainless steel ring. It cannot shift or be displaced during screw driving or under service loads.

Q: Do you provide material test certificates?
A: Yes. Mill certificates, EPDM material data sheets, and RoHS declarations available upon request.

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FULLERKREG Fasteners — Precision DIN Standard Fasteners, Direct from Manufacturer.
For wholesale inquiries, technical questions, or custom orders, please contact our sales team.