Metric thread pitch is a key detail in engineering hardware. It affects how parts fit together, how strong the connection is, and where the fastener should be used. This guide explains metric coarse (standard) and metric fine threads, with practical examples commonly used in engineering hardware across New Zealand.
What Is Metric Thread Pitch?
Thread pitch is the distance between one thread and the next, measured in millimetres. Metric threads follow international ISO standards and are identified by:
- The nominal diameter (for example, M8)
- The thread pitch (for example, 1.25 mm)
If no pitch is shown, the thread is usually metric coarse (also called standard pitch).
Metric Coarse (Standard) Threads
Metric coarse threads are the most common type of metric thread used in engineering hardware.
Key Characteristics
- Wider spacing between threads
- Stronger resistance to damage and dirt
- Easier to assemble and remove
- Compatible with most standard nuts and tapped holes
Common Uses
- General engineering and fabrication
- Construction and infrastructure projects
- Machinery and equipment assembly
- Automotive and trailer hardware
In engineering hardware supplied in New Zealand, metric coarse is considered the default thread type. Unless a product specifically states that it is metric fine, it should be assumed to be metric coarse.
Metric Fine Threads
Metric fine threads use a smaller pitch, meaning the threads are closer together.
Key Characteristics
- More threads per length
- Greater resistance to loosening from vibration
- More precise adjustment capability
- Requires accurate matching components
Common Uses
- Automotive and mechanical assemblies
- Hydraulics and pneumatic fittings
- Applications with limited thread engagement length
- Precision engineering components
Metric fine threads are less common and are typically specified clearly due to compatibility requirements.
Coarse vs Fine: Side-by-Side Comparison
- Coarse pitch: More durable, easier to source, standard for most engineering hardware
- Fine pitch: Better for vibration resistance and precision, but less forgiving
How to Tell What Pitch Your Metric Thread Is
There are several simple ways to identify your thread pitch:
- Check the product description or technical specification
- Measure the distance between threads using a ruler or calipers
- Use a metric thread gauge
- Compare with a known nut or bolt of the same diameter
Important Note on Metric Threads in Engineering Hardware
All metric products supplied by Co-Mac are metric coarse (standard pitch), unless the product details clearly specify that the thread is metric fine. This aligns with common engineering hardware standards used throughout New Zealand.
Why Thread Pitch Matters
Choosing the correct thread pitch ensures:
- Proper fit between components
- Correct load handling
- Reduced risk of thread damage
- Reliable performance in engineering applications
Understanding whether your metric thread is coarse or fine helps avoid mismatches and ensures the right hardware is used for the job.
