Cup Washers
What are Cup Washers?
Cup washers, also called finishing washers, are formed washers with a shallow cup that cradles a screw head. They create a clean finished look, spread load on the surface, and help center the screw during tightening. Often paired with oval head or flat head screws for furniture, cabinetry, and decorative hardware.
What do cup washers do?
- Create a neat, finished appearance around the screw head
- Distribute clamping force to protect wood, plastic, and thin sheet
- Help cover slightly oversized or imperfect holes
- Improve seating of oval head and flat head screws
When should I use a cup washer?
Use a cup washer when the fastener will be visible, when you need extra bearing surface on soft materials, or when you want to hide minor hole irregularities without countersinking the workpiece.
Cup washers vs countersunk holes what is the difference?
A countersunk hole recesses the screw into the material. A cup washer gives a similar low profile without machining the surface, and it can be swapped or refinished later. Choose countersinking for fully flush hardware, and a cup washer for speed, appearance, and material protection.
What size cup washer do I need?
- Choose by screw size, for example #6, #8, #10, or 1/4 in
- Match the washer style to the screw head shape, typically oval head or flat head
- Confirm the inner recess fits the screw head so it seats evenly
- Select thickness that supports the load without deforming the cup
Materials and finishes
18-8 and 304 stainless steel
Clean appearance and dependable corrosion resistance for indoor and light outdoor use.
316 stainless steel
Enhanced corrosion resistance for marine or chemically harsh environments.
Brass
Warm decorative finish that polishes well and conducts electricity for select applications.
Silicon bronze
Marine friendly with a rich tone that ages gracefully on wood and nautical hardware.
Black oxide stainless
Low glare aesthetic for dark hardware sets. Maintain with light oil for best appearance.
Installation tips
- Place the cup washer between the screw head and the surface with the cup facing the head
- Tighten gradually to avoid dimpling thin sheet or crushing soft wood
- Use pilot holes sized for the screw to keep alignment centered in the cup
- For outdoor use, keep materials compatible to limit galvanic corrosion
Common uses for cup washers
- Cabinetry, furniture, and trim work where appearance matters
- Panels, brackets, and nameplates on equipment and fixtures
- Marine and architectural accents with matching metal finishes
- Repairs where a neat cover around the screw head is desired
Best practices and selection tips
- Match finish and material to nearby hardware for a cohesive look
- Select stainless for moisture exposure and brass or bronze for decorative work
- Do not over-torque; the cup should seat evenly without crushing the surface
FAQs about Cup Washers
It provides a finished look around the screw head, spreads load on soft materials, and helps cover minor hole imperfections.
They are commonly used with oval head and flat head screws to create a smooth, centered seat.
Use a countersunk hole for a fully flush head. Use a cup washer when you want a neat recess without machining the surface or when working with thin stock.
Choose by screw size such as #6, #8, #10, or 1/4 in. Confirm the screw head nests in the cup without wobble and that the outside diameter covers the hole.
They increase bearing area and reduce surface crushing, which helps joints in soft materials hold preload more consistently.
Not by itself. Use proper torque and add a locking method if vibration is expected.
Stainless steel is a strong choice for moisture exposure. Use 316 stainless in marine or harsh environments.
When appearance is a priority, especially on woodwork and decorative projects. Both offer a warm tone that complements architectural hardware.
Yes, many finishes accept paint or lacquer. Lightly scuff and clean before coating for better adhesion.
Tighten in small increments and stop once the cup seats evenly. Over-torque can deform the washer or dent the surface.