KEVOS® MAKEOS · Threads
Acme Thread Tap Drill Size
What drilled hole size suits tapping this Acme thread?
Minimum and maximum internal minor diameters, and the drill size range, for tapping general purpose (G) and centralizing (2C–4C and 5C–6C) Acme screw threads by the handbook formulas derived from ANSI/ASME B1.5, with an allowance for drill oversize.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Basic major diameter | in | Basic major diameter of the Acme thread. |
| Threads per inch | Threads per inch. | |
| Class | choice | Thread class (5C and 6C are not recommended for new designs). |
| Probable drill oversize | in | Expected amount the drill cuts oversize (from experience with the drill and material). |
Method and formulas
- Pitch p = 1 ÷ threads per inch.
- General purpose: minimum = D − p. Centralizing 2C–4C: minimum = D − 0.9 p. Centralizing 5C–6C: minimum = (D − 0.025 √D) − 0.9 p.
- Maximum = minimum + 0.05 p; choose a drill whose size plus oversize lies between the limits, close to the maximum.
- Example: ½-10 Acme 2G needs a hole between 0.4 and 0.405 in.
Limitations
- Inch Acme threads to ANSI/ASME B1.5; stub Acme threads differ.
- Actual drill oversize depends on the drill, its sharpening and the material.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose a drill before tapping an Acme thread
- Check a hole size on a drawing
- Allow for drill oversize in selection
Who it is for
- Machinists
- Toolmakers
- Manufacturing engineers
What you get
- Minimum and maximum hole diameter
- Drill size range allowing for oversize
- Values in millimetres
Interpreting the result
- Staying near the maximum limit reduces the material the tap must remove.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 944–947. Topic reference; no source tables or recommended settings are reproduced.
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