The things you need to know about fasteners and washers with RND

What are fasteners?

A fastener is a hardware device that mechanically joins two or more objects together to create a non-permanent joint. Although a small component, fasteners are a crucial element of any structure or machine.

With an extensive range of fasteners available, choosing the best option for your application can be a difficult task. The most common types of fasteners include:

• Screws/bolts
• Nuts

Screws

High quality screws ensure that products can be held together securely through rigorous use. They are ideal for applications such as specialist vehicles, data services, consumer electronics and consumer appliances. Screws offer a number of different features that should be considered when choosing the most appropriate screw for your application.

1. Screw head

The screw head type will be the first feature considered and may be chosen based on personal preference or functionality. For users wanting a flush, flat appearance then a flat countersunk head may be a good choice to achieve this, however, products with thicker walls may require a thicker screw head that can rest on the surface of the product.

Common types of screw head include:

• Washer head
• Rounded head
• Oval-head
• Cylindrical cross-head
• Countersunk cross-head
• Countersunk flat

2. Screw length

Although seemingly self-explanatory, the screw length refers to the distance from the bottom of the screw to the area where the screw would rest on a surface. For some screws the length may include all or some of the screw head and for others it may not include the screw head at all. In the image below, four different types of screw are shown with different screw heads but all with the same screw length.

3. Thread size

The thread of a screw refers to the helical tooth that runs around the outside of the screw shaft. It is the thread that provides the screw with its fastening capabilities and distinguishes it from other fasteners such as nails.

The ISO metric thread standard is the most commonly used standard for measuring screw thread. Displayed as an M size that represents the screw’s nominal size in millimetres, an M3 screw, for instance, will have a 3mm nominal thread diameter.

4. Material

Fasteners are manufactured using a number of materials such as titanium, plastic and steel and, even beyond the material type, can be categorised further according to different grades. They can also be coated in a range of coatings or platings to increase the component’s resistance to corrosion which may be an important consideration depending on the application.

Other considerations include the strength, the brittleness and the cost of a material and the environment of the project.

Nuts

Nuts are used extensively in a number of applications including consumer electronics, appliances, data servers, specialist vehicles and retail displays. Nuts hold components through the friction of the bolt and nut threads when applied against one another.

1. Size

Metric measurements for nut size typically indicate nominal diameter, coarse thread and fine thread, all of which are measured in millimetres. Metric nuts are also available in five different tolerances rated from 4 to 8. The lower the tolerance value, the less tolerance a nut will have. Nuts with higher tolerance values offer greater tolerance for space between the nut and bolt threads.

2. Types of nut

Nuts are available in either “locking” or “non-locking” variations with examples of each including:

Locking	Non-locking
Castle nuts	Acorn nuts
Flange nuts	Anchor nuts
Insert nuts	Cage nuts
Jam nuts	Coupling nuts
Jet nuts	Finger nuts
Kep nuts	Hex nuts
Palnuts	Push nuts
Speed nuts	Square nuts
Split beam nuts	Washer nuts

It is worth noting that two non-locking nuts, when torqued against one another, can create a locking action.

3. Material

Nuts are commonly made from metal but are also available in other materials. The choice of nut material will depend on the application as different materials offer different properties.

• Aluminium- light, resistant to oxidation and with an ability to conduct heat and electricity
• Brass- strong, corrosion resistant, conductive and offers low magnetic permeability
• Copper alloy- offers good load capacity, wear resistance and is suitable for dynamic loads
• Steel- strong, carbonated iron but when uncoated, steel is susceptible to corrosion
• Stainless steel- chemical and corrosion resistant with an aesthetic finish
• Titanium- hard, strong, light and corrosion resistant
• Nylon- tough and resistant material with good pressure ratings
• Plastic- inexpensive and corrosion resistant
• PVC- flexible, smooth and non-toxic, PV nuts are resistant to chemicals
• Rubber- used in specific applications requiring vibration and noise dampening

What are washers?

Washers are placed through the end of threaded fasteners such as screws and bolts, but is not driven into the surface. An important component, the lifespan of products can be dramatically reduced if washers are not used. They are ideal for:

• Load distribution- washers evenly distribute the load of the threaded fastener. This is important as threaded fasteners often stress the material into which they are being driven. By using a washer the risk of damage is reduced as the fastener’s load is evenly distributed across the surface of the material. Washers are not always required but are ideal when used with soft materials such as wood.
• Spacing- if the screw/bolt is longer than the depth of the object that it is being driven in to, then once fully inserted, the threaded fastener will protrude beyond the other side of the object. To avoid this from happening, a washer can be placed on the threaded fastener before it is driven in to the object.
• Absorbing vibration- some washers are designed to absorb vibrations. These are typically made from rubber or plastic rather than metal. This type of washer is ideal where two objects are being connected and one of them produces vibrations as such a washer can ensure that the other object being connected is not damaged.
• Liquid protection- ideal for use in water pipes or environments where a waterproof seal is required, liquid-sealing washers can be secured tightly against an object to prevent the ingress of water and liquids.

It is therefore essential to choose the right washer for your application to ensure optimum use and to maintain the longevity of the products used.

6 common types of washers

1. Flat washers

• Applications: general manufacturing, maintenance and repair
• Uses: ideal for distributing the fastener’s load while reducing heat and friction during the tightening process. Flat washers can also be used to provide electrical insulation and as spacers in some domestic and industrial applications.

2. Lock washers

• Applications: automotive, aerospace and domestic appliances
• Uses: work well with fasteners that tend to rotate or lose friction due to vibration or torque. Lock washers hold the nut and bolt securely in place and so are ideal for transportation industries.

3. Tab washers

• Applications: aerospace and medical applications
• Uses: designed to use flat, lock washers feature single or multiple tabs that are formed to shape around bolts and nuts. Perfect for harsh environments, these washers can endure extreme heat conditions and heavy vibrations.

4. Shoulder washers

• Applications: electronics
• Uses: often used in electronics, shoulder washers are used as a bushing to insulate fasteners and shafts within electronic equipment. Made from non-conductive materials such as nylon, these washers should not be used in humid environments.

5. Countersunk washers

• Applications: furniture, freshwater marine applications
• Uses: enable flat/oval head countersunk screws to be installed flush with the part surface. In addition to functionality, countersunk washers are aesthetically pleasing and so are often used on cabinetry and furniture.

6. Spring washers

• Applications: furniture, freshwater marine applications
• Uses: enable flat/oval head countersunk screws to be installed flush with the part surface. In addition to functionality, countersunk washers are aesthetically pleasing and so are often used on cabinetry and furniture.

Fasteners and washers are simple yet crucial components that every maintenance professional uses on a daily basis. The RND range is ideal with a broad range of fasteners and washers to enhance your applications. These quality components are safety compliant, durable and reliable whilst offering competitive pricing and cost savings compared to other brands.

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