KEVOS® MAKEOS · Threads
Three-Wire Thread Measurement
What should the measurement over three wires read for this thread, or what pitch diameter does a reading give?
Measurement over wires for 60°, 55° and 29° threads from the pitch diameter and wire size, the best wire size, and the pitch diameter from a measured reading.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thread angle | choice | Included thread angle. |
| Pitch | mm or in | Thread pitch in the same unit as the diameters. |
| Pitch diameter (target) | mm or in | Target pitch diameter from the thread limits (e.g. mid-tolerance). |
| Wire diameter (0 = best size) | mm or in | Measured diameter of the wires you will use; 0 calculates with the best wire size. |
| Measured reading over wires (0 = none) | mm or in | Reading over the wires, to convert into a pitch diameter; 0 if not measured. |
Method and formulas
- Best wire W = (P ÷ 2) sec(α ÷ 2) (0.57735P for 60°).
- M = E − (P ÷ 2) cot(α ÷ 2) + W(1 + csc(α ÷ 2)); for 60° this is E − 0.866025P + 3W.
- From a reading: E = M + (P ÷ 2) cot(α ÷ 2) − W(1 + csc(α ÷ 2)).
- Example: pitch diameter 10.863 with 1.75 pitch and best wires (1.0104) reads 12.379 over the wires.
Limitations
- Lead-angle effect is ignored; it is small for single-start fastener threads but matters for multi-start and Acme threads.
- Measuring force and wire accuracy affect the reading; use calibrated wires.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Inspect external threads to their pitch diameter
- Choose wires for a thread
- Convert a wire reading to pitch diameter
Who it is for
- Quality inspectors
- Machinists
- Toolmakers
What you get
- Best wire size
- Expected measurement over wires
- Pitch diameter from the measured reading
Interpreting the result
- Compare the pitch diameter from the reading with the thread class limits.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1990–2003. Topic reference; no source tables or recommended settings are reproduced.
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