Thread Calculator

The Thread Calculator computes the exact dimensions of metric screw threads — the helical ridges that allow bolts and nuts to fasten together — based on ISO standards. Enter your nominal diameter, select a thread pitch, choose External (Bolt) or Internal (Nut), and set your tolerance grade and tolerance position to get the pitch diameter as the primary output. Secondary results include major diameter, minor diameter, thread height, and the standard thread designation string.

mm

Thread Type *

Lower grades have tighter tolerances

Results

Pitch Diameter

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Major Diameter

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Minor Diameter

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Thread Height

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Thread Designation

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Frequently Asked Questions

What are threads and how do they work?

Threads are helical grooves and ridges wrapped around a cylindrical shaft. They convert rotational motion into linear motion, allowing bolts and nuts to be fastened together with mechanical advantage.

How do I calculate the pitch diameter of a thread?

The pitch diameter is calculated as: Nominal Diameter - (0.6495 × Pitch). This is the diameter at the point where the thread thickness equals the groove width.

How do I calculate the minor diameter of a thread?

For external threads: Minor Diameter = Nominal Diameter - (1.2268 × Pitch). For internal threads, it's slightly larger to accommodate tolerances.

What is the difference between external and internal threads?

External threads are found on bolts and screws, while internal threads are found in nuts and threaded holes. External threads have slightly smaller dimensions to allow proper fit.

What do thread tolerance grades mean?

Tolerance grades (4-8) indicate how precise the thread dimensions are. Lower numbers mean tighter tolerances and better fit, while higher numbers allow more variation for easier manufacturing.

What is the nominal diameter of a thread?

The nominal diameter is the basic major diameter of the thread - the largest diameter of an external thread or the theoretical diameter before threading for internal threads.

How do I read metric thread designations?

Metric threads are designated as M[diameter]×[pitch]. For example, M10×1.5 means a metric thread with 10mm nominal diameter and 1.5mm pitch between threads.

What is thread height and why is it important?

Thread height is the radial distance from the minor to major diameter. It determines the strength of the threaded connection and affects how much material is engaged between mating threads.