What’s a cup washer?

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A cup washer is a convex fastener used for support, insulation, or decoration for screws and bolts. It can be surface mounted or countersunk and is made of materials such as steel, brass, plastic, or leather. Cup washers come in various designs and sizes and are used in different applications, including electrical and electronic ones.

A cup washer is a light, convex fastener used as a decorative, insulating or support element for screws and bolts. This type of washer can be used as a countersunk or surface mount item. All types of disc washers feature a bowl-shaped central depression that allows for smooth seating of bolts or screws. A cup washer is usually made of light steel, brass, leather or plastic and comes in a variety of sizes and designs.

A cup washer is generally used to offer support, insulation or an aesthetic finish to bolts or screws, especially those with a countersunk head. Cup washers are made from a variety of materials depending on the intended application. These include light metals such as steel or brass, insulating materials such as plastics and, in the case of washers for faucets and pumps, leather. Cup washers are designed to be surface mounted or countersunk. They often include features such as decorative snap-on caps and cutouts for electrical terminals.

Surface mount cup washer designs resemble a dog’s water bowl with raised sides and a dished center. This type of cup washer is especially good for applications that don’t allow for countersinking screws. The washer therefore offers a good bearing surface for the screw and, as the screw head sits within the washer, a flush and smooth finish. Surface mount washers are usually made of brass or small gauge steel and often feature a decorative cap that encases the screw head.

The flush mounted cup washers are countersunk into the work surface and have internal contours suitable for countersunk or flat head bolts and screws. This type of cup washer often has a lip or flange built into the outer edge to offer better support for the screw. These washers can be made from a variety of materials, including nylon, although steel and brass are the most common. The Flush Mount Cup Washer is commonly used in timber construction and offers a good bearing surface and a smooth finish. This type of washer also often comes with a snap-on cap.

Insulating cup washers are used to electrically insulate metal screw and bolt heads. They are often used to insulate screws used as standoffs on circuit boards and bolts that hold electrical components in place. These washers typically have a flat bottom and high enough sidewalls to offer maximum protection against electrical shorts. Other designs of cup washers in electrical and electronic applications are end cups. These washers have a cutout in the sidewall that allows for tabbed termination terminals

While leather cup washers are rarely used, they are frequently found as gaskets in various applications. These include faucet washers, booster pump seals on kerosene lamps, and small hand pumps or seals on piston-operated air rifles. This type of washer is particularly effective as a seal in environments characterized by exposure to oily fluids. These washers are generally available as a flat disk which is attached to the operating member of the apparatus and cup formed in situ.

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