Short Answer:

Thread pitch is the distance between two corresponding points on adjacent threads. In simple words, it tells how close or far the threads are from each other on a screw, bolt, or nut. It is measured in millimeters for metric threads and as threads per inch (TPI) for imperial threads.

To measure thread pitch, tools like a thread pitch gauge are commonly used. The gauge has several blades with different spacing, which are matched against the threads until the correct one fits perfectly. For precise measurements, vernier calipers or optical methods may also be used.

Detailed Explanation:

Thread pitch and how it is measured

In any threaded component—like a bolt, screw, or nut—there are helical grooves running along the surface. These grooves form the threads, and they help in fastening or adjusting parts by rotating them into a matching component. A key property of these threads is their pitch, which decides how many threads appear along the length and how fast the screw moves when turned.

Understanding thread pitch is very important in mechanical design, fitting, and manufacturing, because choosing the wrong pitch may result in improper fit, failure of the joint, or even damage to the components.

What is thread pitch

Thread pitch is the distance from one thread to the next, measured along the axis of the threaded part.

For metric threads, pitch is given in millimeters (mm), which is the space between two threads.
Example: M8 × 1.25 means an 8 mm diameter screw with 1.25 mm pitch.
For imperial or inch threads, pitch is expressed as TPI (threads per inch).
Example: A 1/4″-20 screw has 20 threads in one inch, meaning each thread is spaced at 1/20 inch.

So, lower pitch means the threads are closer together (fine threads), and higher pitch means threads are farther apart (coarse threads).

Why thread pitch is important

It determines how tightly or loosely a screw fits into its matching nut or hole
It affects the load-carrying strength of the thread
It controls the axial movement per rotation (e.g., fine pitch moves slowly, coarse pitch moves fast)
It ensures compatibility between threaded parts
Different machines and industries follow specific pitch standards for interchangeability

How to measure thread pitch

There are different methods to measure thread pitch depending on the accuracy needed:

Using a Thread Pitch Gauge

This is the most common and simplest method.

A thread pitch gauge is a tool that looks like a folding knife, with multiple blades having teeth of various pitches.
To use it:
1. Select a blade and place it against the threads of the part.
2. Check if the teeth of the blade match perfectly with the thread.
3. If it fits without gaps or overlaps, the number marked on the blade is the thread pitch.

Available for both metric and inch threads.

Using a Vernier Caliper

For a quick manual method:

Select a certain number of thread peaks (for example, 10).
Measure the distance from the first peak to the last peak using a caliper.
Divide the measured distance by the number of threads.
This gives the pitch (for metric) or helps calculate TPI (for inch).

Example: If 10 threads cover 12.5 mm, then pitch = 12.5 mm ÷ 10 = 1.25 mm.

Using an Optical Comparator or Microscope

For high-precision work in industries:

Threads are magnified using a profile projector or measuring microscope.
The pitch is measured using scales on the screen.
Best for very small threads or when extreme accuracy is needed.

Types of thread pitch

Coarse pitch: Fewer threads per unit length, faster to assemble, used for general-purpose fastening.
Fine pitch: More threads per unit length, provides better holding strength, used in precision tools and vibration-prone joints.

Conclusion

Thread pitch is the distance between two threads, and it plays a key role in how a threaded part fits and functions. It can be measured easily using a thread pitch gauge, vernier caliper, or optical tools for high accuracy. Whether in bolt-nut connections, machine components, or precision instruments, knowing and controlling thread pitch ensures safe and proper assembly. Selecting the correct pitch also helps achieve the required motion, strength, and durability in mechanical fittings.