KEVOS® MAKEOS · Threads
Acme and Trapezoidal Thread Dimensions
What are the basic dimensions of this Acme or metric trapezoidal thread?
Basic pitch, minor and major diameters, thread height, crest clearance, lead, lead angle and root area of a general-purpose Acme (inch) or ISO metric trapezoidal (Tr) thread.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thread system | choice | Metric trapezoidal (sizes in mm) or Acme (sizes in inches). |
| Nominal major diameter | mm or in | Nominal (major) diameter in mm (Tr) or inches (Acme). |
| Pitch (trapezoidal) | mm | Pitch in millimetres for trapezoidal threads (ignored for Acme). |
| Threads per inch (Acme) | TPI | Threads per inch for Acme threads (ignored for Tr). |
| Number of starts | starts | Number of starts; lead = starts × pitch. |
Method and formulas
- Tr (ISO 2904): H₁ = 0.5P; crest clearance ac = 0.15 (P = 1.5), 0.25 (2–5), 0.5 (6–12), 1 (14–44) mm; d₂ = d − 0.5P; d₃ = d − 2(0.5P + ac); D₁ = d − P.
- Acme (general purpose): basic height 0.5p; pitch diameter = D − 0.5p; minor diameter = D − p; crest flat 0.3707p.
- Lead angle = atan(lead ÷ π d₂); root area = π d₃² ÷ 4.
- Example: Tr20 × 4 has d₂ = 18 mm and d₃ = 15.5 mm.
Limitations
- Basic dimensions only; class allowances and tolerances (e.g. 7e/7H, 2G/3G) come from the thread standards.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Machine or inspect lead screws and nuts
- Find the root area for screw strength
- Set thread depth for single-point cutting
Who it is for
- Machinists
- Design engineers
- Quality inspectors
What you get
- Pitch diameter
- External minor (root) diameter and internal minor diameter
- Thread height and crest clearance
- Lead, lead angle and root area
Interpreting the result
- Use the root (minor) area for tensile and buckling checks of lead screws.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1921–1946. Topic reference; no source tables or recommended settings are reproduced.
- ISO 2904 Metric trapezoidal screw threads — Basic dimensions; ASME B1.5 Acme screw threads
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