KEVOS® MAKEOS · Threads
Square, Modified Square and 60° Stub Thread Basic Sizes
What are the basic pitch and minor diameters, thread depth, thread thickness and crest and root flats of a square thread, a 10° modified square thread or a 60° stub thread, with my clearance, and what is the lead angle?
Basic dimensions of the alternative power transmission thread forms the handbook gives: square thread h = t = 0.5p, E = D − 0.5p, K = D − p; 10° modified square thread E = D − 0.5p, K = D − p, h = 0.5p, t = 0.5p, crest flat F = 0.4563p and root flat G = 0.4563p − 0.17C; 60° stub thread t = 0.5p, h = 0.433p, F = 0.25p, G = 0.227p, E = D − 0.433p, K = D − 0.866p with a clearance of at least 0.02p added to the depth; and the lead and lead angle for the number of starts.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thread form | choice | Which of the alternative power thread forms is cut. |
| Basic major diameter D | mm | Basic major diameter of the screw. |
| Pitch p | mm | Pitch of the thread. |
| Number of starts | starts | Number of thread starts; the lead is starts × pitch. |
| Clearance added to the depth C | mm | Clearance between the root of the screw and the crest of the nut thread. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Thread form
- What it is
- Which of the alternative power transmission thread profiles is cut.
- Units and format
- Choose one of 3 options from the list: Square thread; 10° modified square thread; 60° stub thread.
- Example
- The form opens with “10° modified square thread” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Sets the depth, flats and pitch diameter formulas.
- Get it right
- The 10° modified square thread is the practical form of a square thread.
What this means: Basic major diameter D
- What it is
- Basic outside diameter of the screw thread.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 2000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The pitch and minor diameters follow from it.
- Get it right
- Use the nominal size from the drawing.
What this means: Pitch p
- What it is
- Axial distance from one thread to the next.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the depth, thickness and flats.
- Get it right
- For inch threads divide 25.4 by the threads per inch.
What this means: Number of starts
- What it is
- How many separate threads run side by side on the screw.
- Units and format
- Enter a number in starts: a number of thread starts. The form accepts 1 starts to 12 starts. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 starts as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The lead and lead angle rise in proportion.
- Get it right
- Count the thread ends at the end of the screw.
What this means: Clearance added to the depth C
- What it is
- Gap left between the screw root and the crest of the nut thread.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.15 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Deepens the thread and narrows the root flat of the modified square form.
- Get it right
- For the 60° stub thread use at least 0.02 times the pitch.
Method and formulas
- Square: h = 0.5p, t = 0.5p, E = D − 0.5p, K = D − p.
- 10° modified square: E = D − 0.5p, K = D − p, h = 0.5p, t = 0.5p, F = 0.4563p, G = 0.4563p − 0.17C.
- 60° stub: t = 0.5p, h = 0.433p, F = 0.25p, G = 0.227p, E = D − 0.433p, K = D − 0.866p; clearance at least 0.02p.
- Depth with clearance = h + C; lead = starts × p; lead angle = atan(lead ÷ π E).
- Example: the screw has a basic pitch diameter of 37 mm and a depth of 3.15 mm with clearance.
Limitations
- These are basic sizes; set allowances and tolerances for the fit you need.
- The nut groove of a square thread is made a little wider than half the pitch to give the screw clearance.
- Consult the cutting tool maker before specifying multiple thread milling cutters or ground taps for modified square threads of large lead angle.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set the basic sizes for turning a square or modified square thread
- Grind a threading tool to the crest and root flats
- Find the lead angle of a multi-start power thread
Who it is for
- Machinists
- Toolmakers
- Machine designers
What you get
- Basic pitch and minor diameters
- Basic depth and depth with clearance
- Thread thickness and crest and root flats
- Lead and lead angle
Interpreting the result
- The modified square thread is the practical equivalent of a square thread that can be produced economically.
- The square thread has largely been replaced by the Acme form.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1944. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Useful alongside · Library collection
Power screws and linear motion: leadscrews, ball screws, linear guides and cams
In Machine Elements and Mechanical Design
What it covers: Turning rotation into accurate straight-line motion is central to machines and automation. How to size leadscrews and ball screws, choose guides and actuators, and design cam motion.
KEVOS® 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 Square, Modified Square and 60° Stub Thread Basic Sizes calculator