Thread pitch defines the distance between adjacent threads on a screw. In the metric system it is expressed as a linear distance in millimetres per thread, while the Unified National Coarse (UNC) and Unified National Fine (UNF) standards use threads per inch (TPI) as the reciprocal measure.
The conversion between these two systems hinges on the fixed relationship that one inch equals exactly 25.4 millimetres. By dividing the inch‑based count by the metric distance, or vice‑versa, a designer can translate a thread specification from one standard to the other.
Because UNC and UNF families contain discrete, standardized TPI values, the raw conversion is usually rounded to the nearest standard size. This ensures compatibility with existing fasteners and tooling while preserving the intended strength and fit.
How do I convert threads per inch (TPI) to millimeters per thread?
What is the formula to convert metric thread pitch to inches per thread?
How many threads are there in an inch for a UNC standard screw?
What is the metric equivalent of UNF (Unified National Fine) thread pitch?
Can you explain the relationship between millimeters and inches in threading?
How do I determine the correct thread pitch for a metric screw?
What is the difference between UNC and UNF threading standards?
Results are for informational purposes only and do not constitute professional advice.