KEVOS® MAKEOS · Threads
Thread Pitch Diameter by Three Wires (Accept or Reject)
Given my reading over three wires, what is the thread’s pitch diameter, and is it within the drawing limits?
Three-wire inspection of a symmetrical external thread: best wire size and the wire constant for the flank angle (as the three-wire tool), the measurement over wires expected at the largest and smallest permitted pitch diameter, the pitch diameter worked back from your reading, and accept or reject against the limits (which you can take from the metric thread limits tool for the class).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thread angle | choice | Included flank angle of the thread. |
| Pitch | mm | Pitch of the thread. |
| Largest pitch diameter allowed | mm | Upper limit of pitch diameter (for example from the metric thread limits tool). |
| Smallest pitch diameter allowed | mm | Lower limit of pitch diameter. |
| Wire diameter used (0 = best size) | mm | Diameter of the wires actually used; 0 uses the best size. |
| Reading over the wires | mm | Micrometer reading over the three wires. |
Method and formulas
- Best wire W = (P ÷ 2) ÷ cos(α ÷ 2); wire constant k = W [1 + 1 ÷ sin(α ÷ 2)] − (P ÷ 2) ÷ tan(α ÷ 2) (as the three-wire tool).
- Over-wire limits M = E + k at the largest and smallest pitch diameter E.
- Measured pitch diameter E = M_read − k; accept when it lies within the limits.
- Example: the reading should lie between 10.161 and 10.293 mm; 10.25 mm gives a pitch diameter of 8.951 mm.
Limitations
- No lead-angle correction; multi-start and coarse threads need it.
- Measuring force and wire accuracy affect the result at the micrometre level.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Inspect a thread with wires and a micrometer
- Set over-wire limits for a thread drawing
- Check a thread between gauges
Who it is for
- Inspectors
- Machinists
- Quality engineers
What you get
- Best wire and the wire constant
- Over-wire limits for the pitch diameter limits
- Pitch diameter from the reading and the decision
Interpreting the result
- Use wires close to the best size so they touch the flanks at the pitch line.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1990–2003, 1867–1912. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Thread Pitch Diameter by Three Wires (Accept or Reject) calculator
