The Importance of Thread Pitch and How to Select the Right Fastener for Secure and Reliable Connections
Thread pitch is one of the fundamental characteristics of screw design. Pitch directly affects the holding power and integrity of threaded assemblies. It is the key to pairing a screw or bolt with a compatible nut and ensuring smooth installation.
Whether you’re working with an automotive, aerospace, or any other application that relies on secure fasteners, selecting the correct thread pitch is critical to avoiding issues like loosening, misalignment of components, premature damage, or mechanical failure.
Here, we’ll go over what thread pitch is and how to select the right pitch for your needs.
So What is Thread Pitch on a Screw?
Holding a screw horizontally, it’s easy to see the peaks and valleys of its profile. The distance between two consecutive peaks is called the pitch, and it represents the distance the screw travels per 360° revolution.
This measurement directly reflects how well the screw or bolt will engage with a corresponding nut or threaded hole. A mismatched pitch between two corresponding fasteners may prevent a screw from engaging, or cause locking or breakage, which compromise the entire assembly.
Generally speaking, the smaller the distance between thread peaks the more fine the threads are. Thread pitch is generally categorized as standard, fine, or extra fine. The finer the pitch, the closer the threads are to each other, which influences how the screw performs under different conditions.
Different screw sizes are often available in a range of pitches. For example, an M12-size screw may have a standard pitch of 1.75mm, a fine pitch of 1.5mm, and an extra fine pitch of 1.25mm.
How to Make Sure You Get the Right Thread Pitch
There are several considerations in selecting the right thread pitch for an application.
Understanding Thread Pitch Systems
Both metric and imperial screws use pitch as a characteristic. Metric thread pitch is measured in millimeters, whereas imperial screw thread pitch is commonly expressed as threads per inch, or TPI. The two systems of measurement can be approximately converted using the equivalent of 2.54 cm per 1 in; however, mixing metric and imperial thread measurements in specifications can lead to mismatched components.
Differentiating Between External and Internal Threads
External threads are found on screws and bolts, while internal threads are located inside nuts or tapped holes. Making sure the thread pitches of external and internal components match is vital for smooth installation and a secure fit.
Measuring and Calculating Thread Pitch
Specialized tools like rulers, calipers, or thread pitch gauges can be used to measure the distance between thread peaks. Thread pitch gauges provide a reliable comparison against the thread, offering more precision than other methods.
Thread pitch can also be calculated with the formula P=L/n, where P is the pitch, L is the thread length, and n is the number of threads.
Selecting the Right Thread Pitch
Consider whether a standard, fine, or custom pitch is needed. Standard pitch is often the default, so be sure to clearly specify the desired pitch if it varies from standard. Custom pitches can be manufactured but may require some lead time.
Different thread pitches have physical characteristics that make them more or less suitable for different applications. Considerations include:
Standard threads:
- Have a larger pitch and are usually more robust for heavy-duty applications
- Resist damage and tearing out of holes
- Install quickly because the screw travels farther with each turn
- Are less likely to lock than finer threads
Fine threads:
- Resist loosening due to vibration
- Can be used for precise adjustments because they travel a small distance with each turn
- Have a shallow thread depth that works well with thin components
- Have a greater risk of locking
Questions? Ask the Sealing Solution Experts at APM Hexseal
APM Hexseal has over 75 years of experience providing high-quality sealing and fastening solutions for many industries including military, medical, and energy generation. Our company holds more than 100 patents including the first self-sealing fasteners, Seelskrews® and Seelbolts®, which are invaluable for environmental protection and leak prevention applications.
We provide a large selection of sealing screws, nuts, washers, bolts, and bushings as well as elastomeric molding capabilities for custom hardware solutions. Our team can help you find the right fasteners for your needs. Contact us with questions or request a quote to get started.
Ever Better.