Stainless Steel Cup Washers

Stainless Steel Cup Washers

We are manufacturers, suppliers, and exporters of Stainless Steel Cup Washers from our precision press shop in India. Stainless steel cup washers are deep-drawn pressed components used as finishing washers under the heads of countersunk screws and bolts in applications where maximum corrosion resistance, longevity, and hygienic finish are required. Also known as SS finishing washers, stainless steel screw cups, stainless steel countersunk washers, A2 cup washers, A4 cup washers, stainless decorative washers, and stainless cup washers for outdoor use, these components provide both a clean, professional finished appearance and the exceptional durability that stainless steel is known for in demanding environments.

While brass and copper cup washers are preferred for decorative and traditional applications, stainless steel cup washers are the first choice for applications requiring maximum resistance to corrosion in outdoor, marine, food-processing, pharmaceutical, and highly humid environments. Grade A2 stainless (SS304 / 1.4301) provides excellent atmospheric and freshwater corrosion resistance. Grade A4 stainless (SS316 / 1.4401) with its molybdenum content provides the highest corrosion resistance, essential for saltwater, chemical, and coastal environments.

Types of Stainless Steel Cup Washers We Manufacture

Standard A2 Stainless Steel Cup Washers (SS304): The most widely used stainless cup washer, suitable for general outdoor, garden, and non-marine applications. Compatible with A2 stainless steel countersunk screws for a fully stainless fastenings assembly. Available for imperial screw sizes No. 4 to No. 14 and metric sizes M3 to M8.

A4 Stainless Steel Cup Washers (SS316): Grade 316 cup washers for marine, coastal, chemical, and offshore applications. The molybdenum in A4 stainless provides resistance to chloride pitting that A2 cannot offer. These are the specification for any boat, marina, waterfront, or coastal building application.

Deep Profile Stainless Cup Washers: Taller cup profile for use with long-shank or high-head countersunk screws in thick material assemblies. The deeper cup provides a more prominent and decorative appearance.

Wide-Flange Stainless Cup Washers: Larger outer diameter cup washers for use in soft or laminated materials where the load must be spread over a greater bearing area to prevent pull-through.

Mirror-Polished Stainless Steel Cup Washers: Highly polished (No. 8 mirror finish) stainless cup washers for premium applications in architectural hardware, interior design, and high-specification joinery where a mirror-bright stainless appearance is specified.

Brushed Finish (No. 4) Stainless Cup Washers: Brushed directional finish cup washers for use with brushed stainless hardware in kitchens, bathrooms, and commercial interiors where a consistent satin-brushed appearance is preferred.

Electropolished Stainless Cup Washers: Ultra-smooth electropolished surface for pharmaceutical, biotech, and ultra-hygienic applications where surface roughness must be minimised and the component must be fully cleanable with sterilisation agents.

Materials – A2 (SS304) and A4 (SS316)

A2 Stainless Steel (304 / 1.4301): 18% Chromium, 8% Nickel austenitic stainless steel. The most widely specified stainless grade, with excellent corrosion resistance in outdoor, industrial, and freshwater environments. Yield strength approximately 210 MPa, tensile strength 515–720 MPa. Suitable for most applications outside of marine and chloride-rich environments.

A4 Stainless Steel (316 / 1.4401): 16–18% Chromium, 10–14% Nickel, 2–3% Molybdenum austenitic stainless steel. The molybdenum substantially increases resistance to chloride pitting, making A4 the specification for marine, coastal, pool, chemical, and food-processing environments. Yield strength approximately 210 MPa, tensile strength 515–690 MPa.

Dimensions and Screw Size Compatibility

Our stainless steel cup washers are manufactured for the following countersunk screw standards: Imperial (UNC/UNF/BSW/BSF): No. 4, No. 6, No. 8, No. 10, No. 12, No. 14 countersunk screws. Metric (ISO): M3, M4, M5, M6, M8, M10 countersunk screws. Countersunk angle: 90° (metric/ISO standard) as default; 82° (imperial/American standard) available on request. Outer diameter range: 10 mm to 38 mm. Material thickness: 0.6 mm to 1.2 mm stainless steel strip, depending on screw size and cup depth.

Manufacturing Process

Stainless steel cup washers require more careful tooling and press setup than brass or copper versions due to stainless steel’s higher strength, work-hardening behaviour, and greater spring-back after forming. Our tooling uses precisely controlled draw reductions, optimised blank-holder pressure, and quality stainless strip with consistent mechanical properties to produce cup washers with accurate profiles, consistent wall thickness, and defect-free surfaces. Polishing and brushing operations are performed on our automated finishing equipment. Electropolishing is carried out in our in-house electrolytic polishing facility.

Applications

Stainless steel cup washers are used in: marine boat building (GRP, aluminium, and wooden boats), coastal and offshore structure assembly, garden furniture and outdoor wooden decking, swimming pool surround construction, food processing equipment assembly, pharmaceutical and cleanroom equipment, bathroom and kitchen fittings, facade and cladding fixings, solar panel frame assembly, agricultural equipment, medical device enclosures, and anywhere that countersunk screws in a wet, humid, or corrosive environment must be finished neatly with a long-service-life component.

Related Products and Search Terms

Stainless steel cup washers are frequently ordered alongside: stainless steel countersunk screws, stainless steel flat washers, stainless steel spring washers, A4 stainless screws, stainless penny washers, stainless wood screws, brass cup washers, copper cup washers. Search terms: stainless steel cup washer, SS cup washer, A2 cup washer, A4 cup washer, SS304 cup washer, SS316 cup washer, marine stainless cup washer, stainless finishing washer, stainless screw cup, stainless countersunk washer, stainless cup washer #8, stainless cup washer M5, stainless cup washer M6, brushed stainless cup washer, mirror polished stainless cup washer, outdoor stainless cup washer, stainless cup washer manufacturer India, A4 marine cup washer.

Why Choose Our Stainless Steel Cup Washers?

We manufacture stainless steel cup washers from certified A2 and A4 stainless steel strip, with pressing, polishing, and surface finishing all performed in-house. Our ISO 9001 quality system ensures consistent dimensional accuracy and surface quality across every production batch. We supply in bulk for trade and wholesale customers, with custom sizes, special finishes, and non-standard screw sizes available on request. Our export capability serves marine hardware distributors, joinery suppliers, and building products wholesalers worldwide.

Frequently Asked Questions (FAQ) – Stainless Steel Cup Washers

What is the difference between A2 and A4 stainless steel cup washers?

A2 (SS304) cup washers are suitable for most outdoor and general applications. A4 (SS316) cup washers contain molybdenum which provides significantly better resistance to chloride-induced pitting corrosion, making A4 the required specification for marine, coastal, saltwater, pool, and chemical environments.

What screw sizes do stainless steel cup washers fit?

We manufacture stainless cup washers for imperial screw sizes No. 4 to No. 14 and metric sizes M3 to M10. Both 90° (metric) and 82° (imperial) countersunk angles are available.

Are stainless steel cup washers suitable for decking and outdoor timber?

Yes, A2 stainless cup washers are widely used for composite and hardwood decking with countersunk deck screws. For tropical hardwoods containing high levels of tannins or chlorides (such as Ipe and teak), A4 (SS316) is recommended to prevent any staining from galvanic reactions between the fastener and the wood chemistry.

Can stainless steel cup washers be used in GRP (fibreglass) boat construction?

Yes, A4 stainless steel cup washers are extensively used in GRP boat construction for countersunk fastenings through deck hardware, hatches, cleats, and interior fittings. The A4 grade ensures no rust staining on the white GRP gelcoat surface even in a saltwater marine environment.

Do you supply electropolished stainless steel cup washers?

Yes, electropolished stainless cup washers are available in A2 and A4 grades. Electropolishing removes the surface layer of the stainless steel, creating an ultra-smooth, passive surface that is highly resistant to corrosion and easy to clean. Required in pharmaceutical, food, and medical device applications.

What is the minimum order quantity for stainless steel cup washers?

For standard A2 stainless cup washers in stocked sizes, minimum order is 100 pieces per size. For A4 grade or special finishes (mirror, brushed, electropolished), minimum order is 500 pieces. Small sample quantities for approval are available.

Can you make stainless steel cup washers to a custom outer diameter?

Yes, custom outer diameters are available with a minimum order quantity. We can produce cup washers with any outer diameter from 10 mm to 50 mm and custom countersink profiles to match non-standard screw head geometries.

Do you export stainless steel cup washers?

Yes, we export stainless steel cup washers globally to marine hardware distributors, decking suppliers, building products wholesalers, and joinery hardware suppliers in the UK, Australia, USA, New Zealand, UAE, and Europe.

Request a Quote for Stainless Steel Cup Washers

Sourcing A2 or A4 Stainless Steel Cup Washers for your marine, decking, GRP boat building, or outdoor construction project?

📧 Email us at: sales@brass-copper-parts.com with your screw size, stainless grade (A2/SS304 or A4/SS316), surface finish (2B/brushed/mirror/electropolished), and required quantity

📱 WhatsApp/Call: +91-22-43449300 for technical advice on grade selection for your environment, countersink angle requirements, and availability of non-standard sizes

🌐 Visit our facility: See our stainless steel deep-draw pressing and surface finishing capabilities including electropolishing for pharmaceutical and food applications

📋 Request samples: A2 and A4 stainless cup washers in standard screw sizes available for marine fitting, decking, and construction approval testing

Brass & Copper Parts manufactures stainless steel cup washers in A2 and A4 grades for marine hardware distributors, decking suppliers, boatbuilders, and building products wholesalers globally. Contact us today for competitive pricing and full material certification.