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How to determine the pitch of a bolt or nut

    Metric Thread Pitch

    There is a considerable difference between Metric fasteners and Imperial fasteners. They are not interchangeable. One cannot fit a similar-sized metric bolt into an imperial nut otherwise the nut and the bolt would be permanently damaged. Metric screws use a Thread Pitch whereas Imperial screws use ‘Threads Per Inch’ (TPI). Metric Thread Pitch is calculated by measuring the distance between two thread peaks in mm. There are generally two metric threads as shown in the table i.e. Standard/Coarse thread and fine thread.

    Metric Thread Pitch of a bolt

    Metric Thread Drawing

    Using the M5 screw example as shown in the above image, the screw has a Thread Pitch of 0.8mm. It’s easier to count the distance between 10 threads with a vernier and a magnifying glass as shown in the above image rather than trying to measure the spacing of one thread accurately. After measuring the distance between 10 peaks move the decimal point over one space which will give you the pitch. One can also use a thread gauge for accurate results as shown below. 

    Metric Thread Pitch Table

    Screw SizeMetric Thread Pitch (mm.)
    Standard / CoarseFine
    M1.60.35
    M20.40
    M2.50.45 –
    M30.50 –
    M3.50.60 –
    M40.70 –
    M50.80 –
    M61.00 –
    M81.251.0
    M101.501.25
    M121.751.50
    M142.001.50
    M162.00 
    M182.50 
    M202.50 

    Understanding different thread types is important for any tradesman. As an apprentice, you would be asked to locate different nuts and bolts for a particular job. It’s important not to mix them up otherwise it could cause permanent damage. These are some of the basics that are taught in Certificate 2 in Electrotechnology at Ausinet. For someone wanting to make a start in the electrical industry, it would be important to understand the difference in various sizes of nuts, bolts, types and sizes of wires and cables. For further information refer to the blog “Difference between Imperial and metric bolts” and “Metric and Imperial wire sizes”

    Published: 16/01/2024

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