It might seem simple, but much consideration should go into choosing the ideal fasteners for any application. This includes basics such as size, dimensions, load, material, environmental, cost considerations — and more.
Compliance with industry standards is a must to ensure reliability and safety. Understanding the load and stress the fastener will endure is essential as different fasteners have varying load-bearing capacities. Additionally, knowing the weight of the materials to assemble also offers better accuracy in terms of which fastener is suited to an application. And, if using threaded fasteners, selecting the correct thread size is critical if using threaded fasteners.
Threaded fasteners are designed with helical ridges, known as threads, along their shaft, which grip and secure materials together. Threaded nuts, screws, bolts, etc., provide an excellent clamping force, making them ideal for applications where a strong and secure connection is necessary. They can also be adjusted, which is useful when alignment is critical.
Threaded fasteners can be used with thread-locking compounds to prevent loosening from applications with vibrations or dynamic loads. They can also be removed and reinstalled without damaging the materials, making them a good choice when maintenance or repairs are likely.
Choosing a threaded fastener for an assembly depends on the requirements of that application, including its load-bearing capacity, material, environmental conditions, and the desired level of permanence in the connection. Of course, choosing the correct threaded fastener also means choosing the correct thread size.
To start, it’s important to know the thread size and pitch, which vary depending on the fastener type and size. The thread size relates to the nominal diameter of the thread, typically denoted by a number or a combination of letters and numbers. The thread pitch refers to the distance between corresponding points on adjacent threads.
A fastener’s thread and pitch size are critical factors that collectively influence its performance in terms of strength, load-carrying capacity, ease of installation, resistance to vibration, and more. A thread gauge can help measure the size and pitch of existing threads. They’re available for metric and imperial threads.
Always consult the manufacturer’s fastener guide to ensure the correct choice. Most contain charts and information on thread sizes for the different types of fasteners. Also, if the fastener is part of a system or machinery, follow the manufacturer’s recommendations for thread size to maintain compatibility and performance.
Here are a few other tips to consider when deciding on a fastener’s thread:
- The material of both the fastener and the application should influence the fastener’s thread selection. For example, heavier-duty applications typically require larger and stronger threads. Some materials also have better resistance to wear and tear when used with a specific thread pitch.
- The strength requirements are essential to consider when determining the fastener’s thread. Larger thread sizes are typically used in higher stress or vibration applications to ensure the fastener can handle the load. This is common in construction, automotive, or other structural applications.
- If the joint will be subject to heavy loads, a coarser thread pitch may be preferable for its higher load-bearing capacity. A finer thread pitch may be more suitable for applications requiring fine adjustments.
- Consider the environmental conditions to which the threaded connection will be exposed. Generally, coarser threads are more resistant to contaminants and debris in specific environments, while finer threads might be preferred in more controlled conditions.
- When possible, test the selected fastener and thread size in a non-critical application before full implementation. This can help ensure the size meets the performance requirements.
- Note: the torque required to tighten or loosen a threaded connection is influenced by the thread pitch. Coarser threads often require higher torque for a given axial load than finer threads.
- Consider standard fastener sizes when they meet an application’s requirements, which are often more cost-effective and readily available than custom sizes.
Also, threaded fasteners are not always the ideal choice, especially for certain complex or large-scale installations. Threaded fasteners can be more time-consuming to install than non-threaded ones. Also, care must be taken to avoid cross-threading, which can damage the fastener and materials. Threaded fasteners can be more costly than non-threaded alternatives.
Fasteners ensure an assembly remains assembled, which is critical. As such, it’s worth consulting engineering resources or professionals who can provide guidance based on an application’s requirements.