Washer And Screw: Perfect Match For Size And Fit

Matching the correct washer size to a screw is an important step in any building or repair project. Washers are thin plates with a hole in the centre, usually made of metal, plastic, or rubber, and are used to distribute the load of a threaded fastener, such as a screw or nut, evenly over a surface. When matching a washer to a screw, the diameter of the screw shaft should correspond to the inner diameter of the washer. For example, a 3/4-16 bolt should be matched with a 3/4 washer. The inner diameter of the washer will be slightly larger than the bolt diameter, allowing the washer to fit around the bolt. It is also important to consider the grade of the washer, as washers are classified as unhardened or hardened, with the latter typically being of better quality.

Matching the inner diameter of the washer to the shaft of the screw or bolt

When working with screws, bolts, washers, and nuts, it's important to understand how to match the correct parts together. This is especially true when it comes to matching the inner diameter of a washer to the shaft of a screw or bolt. Here are some detailed instructions and considerations to help you with this process:

Understanding Washers

Washers are thin, flat rings, usually made of metal, rubber, or plastic. They are placed under the head of a bolt or nut, or between two joining surfaces. Their purpose is to spread the pressure and distribute the load when tightened. Washers also help to reduce friction, provide insulation or lubrication, and can act as spacers or seals.

Matching Washers to Screws or Bolts

When matching a washer with a screw or bolt, the diameter of the shaft of the screw or bolt (also known as the major diameter) should correspond to the inner diameter of the washer. For example, a 3/4-16 bolt should be paired with a 3/4 washer. The inner diameter of the washer will be slightly larger than the bolt's diameter, allowing the washer to fit snugly around the bolt.

Standard Size Charts

To make things easier, standard size charts are available that specify the correct washer size for a given bolt or screw size. These charts typically list the diameter of the bolt or screw, followed by the corresponding washer size. It's important to select the correct washer size to ensure a secure and proper fit.

Measuring Washers and Bolts

If you need to measure a bolt manually, it is recommended to use a micrometer or bolt gauge. To determine the diameter, measure the distance between the outer threads on both sides of the bolt, excluding the head. When measuring washers, you can use calipers or a ruler to determine the inner diameter.

Special Cases: Fender Washers

Fender washers are an exception to the standard sizing rules. They are designed to allow for two size options: the nominal inner diameter (which matches the bolt diameter) and the outer diameter of the washer itself. For example, a 1/4 x 3/4 fender washer has an inner diameter of 1/4 inch and an outer diameter of 3/4 inch.

Additional Considerations

When working with washers, bolts, and screws, it's important to consider other factors such as thread pitch, material, finish, and thread type. These factors can impact the performance and compatibility of the fastener assembly. Always refer to standard size charts or seek expert advice if you are unsure about matching washers to screws or bolts.

Washer and screw size standards: USS, SAE, and F436

USS, SAE, and F436 are three standards for washer and screw sizes. USS (United States Standard) washers are general-purpose washers for construction and manufacturing. They have a larger outer diameter than SAE washers, which allows them to protect the component better. They also have a larger inner diameter (ID) and outer diameter (OD) than SAE washers. USS washers fit loosely on the screw or bolt and are commonly found in hardware stores, making them suitable for most construction projects.

SAE washers, on the other hand, have a smaller outside diameter and fit tighter on the fastener. This type of washer is often used in machine and automotive applications where tighter tolerances and space limitations are factors. SAE washers are classified as unhardened and hardened, with the latter being of higher grade and better quality.

F436 washers are hardened steel washers used with most high-strength bolts and F1554 anchor bolts. They are typically used with any bolts other than low-carbon steel bolts. F436 washers have a slightly larger ID and OD than SAE washers because they are designed to be used with matching heavy hex structural bolts and nuts. These washers always come hardened and usually bear the F436 designation stamp. While F436 washers are smaller than standard F844 flat washers, they provide higher strength by being through-hardened or carburized.

Choosing the correct washer for the bolt selected

Washers are critical for guaranteeing the integrity and lifespan of attached connections. They are thin plates with a hole in the centre, typically made of metal, plastic or rubber. When choosing the correct washer for the bolt selected, there are several factors to consider.

Firstly, you must consider the material you are working with. The purpose of a washer is to help threaded fasteners do a more reliable job while protecting the surface from damage during tightening. If the fastener is being driven into a weaker material, a washer is necessary to prevent the fastener from distorting the material. In this case, you will need a large bearing surface, which the washer provides. If the fastener and the material are the same, such as metal to metal, a washer is not necessary, but certain types of washers can still be advantageous, such as a lock washer, to prevent the fastener from loosening.

Secondly, you should consider the size of the washer in relation to the bolt. The size of a washer indicates the size bolt that it fits, so you will choose your washer hardware to match the diameter of the bolt. The diameter of the shaft of the bolt should be matched to the inner diameter of the washer. For example, a 3/4-16 bolt should be matched with a 3/4 washer. The inner diameter of the 3/4” washer will be slightly larger than 3/4”, allowing the washer to fit around the bolt.

Thirdly, consider the type of washer you require. There are many different types of washers, each designed for a specific purpose. The most common type is the flat washer, which is used to distribute weight, minimise friction and protect the surface. Flat washers are available in a variety of sizes to accommodate various bolt diameters. Other types of washers include split lock washers, serrated lock washers, wave washers and Belleville washers. Split lock washers, also known as spring washers, feature a split or helical cut that creates tension and prevents nuts and bolts from loosening. Serrated lock washers have teeth that bite into the material and fastener, providing a locking action. They are often used in applications that require high vibration resistance. Wave washers are used to absorb shock, maintain tension and reduce vibration, and are frequently used in the automotive and aerospace industries. Belleville washers, also known as conical spring washers, are conical in shape and are used to produce large spring loads in small places.

Finally, consider the environment in which the washer will be used. Washers are available in different materials, such as metal, rubber and plastic, each with its own advantages and disadvantages. Metal washers are ideal when high strength is needed, while rubber washers offer flexibility and a tight seal, making them suitable for irregular surface areas. Plastic washers are perfect for smaller applications, such as electronics, where resistance to vibrations is required.

Matching the washer size to the screw diameter

To determine the correct washer size, start by measuring the diameter of the screw. This can be done using a caliper or a screw gauge. Once you have the screw's diameter, you can select a washer with a matching inner diameter. It's important to note that washer sizes are typically designated by the diameter of the fastener they are designed to be used with. So, a 3/8" washer is designed to fit a 3/8" screw.

In addition to the inner diameter, washers also have an outer diameter (OD) and a thickness. These dimensions can vary, even for washers with the same inner diameter. For example, a 3/8" USS (United States Standard) washer has an OD of 1" while a 3/8" SAE (Society of Automotive Engineers) washer has an OD of 13/16". So, when selecting a washer, it's important to consider not just the screw size but also the specific application and space limitations.

Another factor to consider is the grade of the washer. Washers are typically classified as unhardened or hardened. Unhardened washers, made of low carbon steel, often have surface imperfections and thickness variations. Hardened washers, on the other hand, are heat-treated and will have a manufacturer's stamp on them, indicating a higher quality product. Matching the grade of the washer to the type of fastener and the application is crucial for ensuring a secure connection.

Lastly, there are different types of washers available, each designed for specific applications. For example, a plain washer is a flat disc used to distribute loads, while a lock washer has internal teeth that dig into the bearing surface to prevent loosening in high-vibration applications. Choosing the right type of washer, in addition to matching the washer size to the screw diameter, is essential for the success of any project.

Using the right screw washer for your project

When building or repairing something, having the right screw washer is essential. Screw washers are designed to hold different types of surfaces together and fit different sizes of screw or bolt heads, so it's important to ensure you have the correct one for your project.

Types of screw washers

A washer is a thin plate with a hole in the centre, typically made of metal, plastic or rubber. Its primary purpose is to distribute the load of a threaded fastener, such as a screw or nut, evenly over a surface. Washers also prevent loosening by preventing metal-to-metal contact between the fastener and the attached surface. The most common type of washer is the flat washer, but there are several other types, including:

• Plain washers: These are flat discs with a centrally located hole. They are used to distribute loads of threaded fasteners, such as screws and nuts, and can also be used as spacers.
• Lock washers: These have internal teeth that dig into the bearing surface, creating friction and preventing loosening. They are often used in high-vibration applications.
• Star washers: These have radial teeth that cut into the bearing surface and are used in applications where there is no need for frequent disassembly and reassembly.
• External tooth lock washers: These have external "teeth" and are used to prevent nuts and bolts from backing out.
• Internal tooth lock washers: These have internal "teeth" and, like the external tooth variety, are used to prevent nuts and bolts from backing out.
• Dock washers: These have a large outside diameter and are thicker than standard washers.
• Ogee washers: These are thick, with larger diameters and a curved or sculpted appearance. They are typically used in wood construction.

Choosing the right screw washer

When choosing a screw washer, there are several factors to consider:

• The material you'll be using the screw washer with
• The environment the screw washer will be used in
• The size and shape of the screw washer
• The finish of the screw washer
• Whether you need a standard or special-purpose screw washer
• Your budget
• Whether you need a custom or stock screw washer

Matching screw and washer sizes

When it comes to matching screw and washer sizes, it's important to remember that the washer must always be larger than the exact diameter of the screw. The size of the washer refers to the nominal inner diameter of the washer and the bolt diameter it is designed to work with. For example, a 3/8-inch USS flat washer has an inner diameter of 7/16 inch and an outer diameter of 1 inch, but it is referred to as a 3/8 washer because it is designed to be used on a 3/8 fastener.

To determine the correct size of washer for your screw, first measure the diameter of your screws. Once you have that measurement, you can select a washer that is slightly larger. For example, if your screws are 1/4-inch in diameter, you would need a 3/8-inch washer.

By choosing the right screw washer and ensuring it matches the size of your screw, you can ensure your project is a success.

Frequently asked questions