KEVOS® MAKEOS · Threads
Buttress Thread Wire Inspection (7°/45° Form, Wire Size, Readings, Pitch Diameter)
For this 7°/45° buttress thread, what are its diameters, what wire size and reading over wires should I use, and does my measured thread pass?
Three-wire inspection of an external 7°/45° buttress thread: the basic form and the internal and external major, pitch and minor diameters with any allowance (as the buttress thread tool), the wire size that touches at the pitch line and the reading over wires at the largest and smallest allowed pitch diameter (as the taper and buttress three-wire tool), and the pitch diameter from your measured reading against your tolerance.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Basic major diameter | mm | Basic major diameter of the thread. |
| Pitch | mm | Pitch (25.4 ÷ threads per inch). |
| Allowance on the external thread | mm | Allowance on the external thread from its class (0 for basic size). |
| Pitch diameter tolerance (below the largest) | mm | How far below the largest pitch diameter the external thread may be (your class tolerance). |
| Wires | ||
| Wire diameter (0 = pitch-line size) | mm | Diameter of the wires you have (0 uses the size that touches at the pitch line). |
| Measured reading over wires | mm | Micrometer reading over the three wires. |
Method and formulas
- h = 0.6p; internal pitch E_n = D − h; external pitch E_s = D − h − G; external minor K_s = D − 1.32542p − G (as the buttress thread tool).
- Included angle 52° with a 7° load flank: wire = p cos 7° ÷ (1 + cos 52°); M = E − [p ÷ (tan 7° + tan 45°) − W (1 + cos 19° ÷ sin 26°)] (as the taper and buttress three-wire tool).
- Pitch diameter from a reading = M + the same constant, against E_s − tolerance to E_s.
- Example: external pitch diameter 48.26 mm; read 52.699 to 52.579 mm over 2.6005 mm wires; 52.65 mm gives 48.211 mm.
Limitations
- Single-start thread; the lead-angle effect is ignored.
- Wires must touch both flanks; very small or large wires sit on the crest or root.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Inspect a buttress thread on a press screw, breech or vice
- Set the wire readings before cutting a buttress thread
- Check a worn buttress screw
Who it is for
- Inspectors
- Machinists
- Toolmakers
What you get
- Thread form and diameters
- Wire size and readings at the pitch diameter limits
- Pitch diameter from the reading and the decision
Interpreting the result
- The load is carried on the 7° flank, so wear shows mainly there; one reading over wires averages both flanks.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1945–1952, 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.
