Cup / Finishing Washer

What a cup washer does

A cup washer (also called a finishing, countersunk or recessed washer) is a dished washer that a countersunk screw head sits down into. It gives the head a neat seat on a flat surface without countersinking the material, spreads the screw's load, and leaves a tidy finished look where the screw shows. Hobson lists its black nylon finishing washer for countersunk head metal thread screws, and says it protects different surfaces and can be used for electrical insulation.

Typical uses are visible screws on cabinetry, furniture, trims, panels and access covers, where a plain countersunk head would sit proud or bite into the surface.

Which cup washer: stainless or nylon?

• •304 stainless cup washers: for 6 to 14 gauge countersunk screws, such as wood screws and self-tapping screws. A bright metal finish that suits stainless screws, indoors or out, though not within 2m of a pool, where Hobson's corrosion guide calls for 316 stainless, which this range does not include.
• •Black UV stable nylon finishing washers (RCC): for M3 to M8 countersunk machine screws. Black nylon has carbon black added for outdoor weathering, so use it outside.
• •Natural nylon cup washers: M3 to M8, for indoor work where you want insulation or surface protection.
• •Skid plate cup washers: 304 stainless, 38mm across, for M6 and M8 bolts. Hobson makes them for 4mm (0.16 inch) and thicker skid plates, the armour plates that shield the underside of an all-terrain vehicle's engine, control arms and drive shaft off-road.

Cup washer sizes

Every cup washer we carry. Gauge sizes suit screws of that gauge (6g, 8g and so on); M sizes suit metric screws. Select a size to open it in the selector.

304 stainless and nylon

• •304 stainless: needs only light care; wash off grime and salt so it stays bright. Rust spots on stainless usually come from carbon steel contamination, such as grinding dust or filings from nearby work, so keep it clean. Very harsh spots, such as surf beach frontages, need more care: ask us before you order.
• •Nylon: Hobson calls PA6.6 (nylon 66) the standard polymer in its nylon range, and lists nylon for protecting surfaces, good electrical insulation and absorbing shocks and vibration. Its nylon properties sheet gives PA6.6 a working temperature of -30 to +100°C; that is a figure for the material, not a rating of a washer. Nylon absorbs moisture from the air, which makes it less stiff and more impact resistant.

Fitting cup washers

1. Match the washer to the screw: the gauge or metric size, and a countersunk head.
2. Drill the hole for the screw; you do not need to countersink the material.
3. Put the washer on the screw with the cup facing up, so the head sits down into it.
4. Tighten until the head sits snugly in the cup. Do not overtighten, especially with nylon washers, or the cup will deform.

Cup washers in Adelaide

Allmat supplies cup washers, countersunk screws and fixings to cabinet makers, builders, mechanics and trade across Adelaide and South Australia. Add the washers to a quote with the screws they go with, and we will price the lot.

Questions