KEVOS® MAKEOS · Threads
Three-Wire Measurement of Taper and Buttress Threads
What should the measurement over three wires be for this taper or buttress thread, and what pitch diameter does a reading give?
Measurement over wires for taper screw threads (corrected for the taper, including the simplified form for American pipe threads) and for buttress threads of any flank angles, the pitch diameter equivalent to a measured value, and the wire size for pitch-line contact on buttress threads.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thread | choice | Kind of thread. |
| Pitch diameter at the measuring point | mm | Pitch diameter where the single wire is placed. |
| Pitch | mm | Pitch. |
| Wire diameter | mm | Diameter of the wires used. |
| Included thread angle (taper) | ° | Included angle of a symmetrical taper thread (60° for pipe threads). |
| Taper on diameter per foot (taper) | mm/ft | Taper on diameter per foot of length (¾ in. = 19.05 mm for American pipe threads). |
| Included angle of the buttress thread | ° | Included angle of the buttress thread groove. |
| Front (load) face angle from the perpendicular | ° | Angle of the front, load-carrying face from the perpendicular to the axis. |
| Measured value over wires (0 = none) | mm | A measured value over the wires, to convert back to pitch diameter. |
Method and formulas
- Taper: M = [E − (cot a) P ÷ 2 + W (1 + csc a)] ÷ sec b, with a half the thread angle and b half the taper angle; for pipe threads M = [E − 0.866025 P + 3W] ÷ 1.00049.
- Buttress: M = E − P ÷ [tan a + tan(A − a)] + W [1 + cos(A ÷ 2 − a) csc(A ÷ 2)].
- Buttress wire for pitch-line contact: W = P cos a ÷ (1 + cos A).
- Example: the handbook 3-in. pipe thread gauge (3.3885 in. pitch diameter, 8 threads per inch, 0.07217 in. wires) measures 3.495 in. over wires.
Limitations
- The taper formula is accurate for tapers up to ¾ in. per foot.
- Wire placement on a taper thread must be at the point where the pitch diameter is wanted.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a taper pipe thread gauge or part over wires
- Measure a buttress thread’s pitch diameter
- Choose wires for buttress thread measurement
Who it is for
- Quality inspectors
- Machinists
- Gauge makers
What you get
- Measurement over wires
- Pitch diameter for a measured value
- Recommended wire size (buttress)
Interpreting the result
- Use the converted pitch diameter to judge the part against its tolerance, not the raw measurement.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2005–2007. 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 Three-Wire Measurement of Taper and Buttress Threads calculator
