BIZOMAT MAKEOS · Quality
ISO Limits of Size and Fit from the Fundamental Deviations
From the fundamental deviation and IT grade I read from the ISO limits tables (with the delta value where it applies), what are the limits of size of my hole and shaft, and what clearance or interference does the fit give?
Limits of size by the BS ISO limits and fits procedure the handbook gives: for a shaft, ei = es − IT when the upper deviation es is tabulated or es = ei + IT when the lower deviation ei is; for a hole, EI = ES − IT or ES = EI + IT, with the delta value added to ES for holes K, M and N up to IT8 and P to ZC up to IT7; H and h have a zero deviation and Js and js are split equally about the basic size; and the largest and smallest clearance of the fit.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Basic size | mm | Basic size common to the hole and the shaft. |
| Hole deviation from the table | choice | Which deviation the hole table gives for its letter. |
| Hole deviation from the table | µm | The tabulated hole deviation, with its sign. |
| Hole IT value from the table | µm | Standard tolerance for the hole grade and size. |
| Delta value Δ for the hole (0 if none) | µm | Delta value from the table for K, M, N up to IT8 and P to ZC up to IT7, or 0. |
| Shaft deviation from the table | choice | Which deviation the shaft table gives for its letter. |
| Shaft deviation from the table | µm | The tabulated shaft deviation, with its sign. |
| Shaft IT value from the table | µm | Standard tolerance for the shaft grade and size. |
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: Basic size
- What it is
- Nominal size common to the hole and the shaft of the fit.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 3150 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 45 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The limits are this size plus the deviations.
- Get it right
- Use the size on the drawing, e.g. 45 for 45 H7/p6.
What this means: Hole deviation from the table
- What it is
- Which of the two hole deviations the ISO table gives for the hole letter.
- Units and format
- Choose one of 4 options from the list: Lower deviation EI given (A to H); Upper deviation ES given (J to ZC); H (EI = 0); Js (± IT ÷ 2).
- Example
- The form opens with “H (EI = 0)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Decides how the other deviation is found.
- Get it right
- Holes A to H have a tabulated EI, J to ZC a tabulated ES; choose H or Js directly.
What this means: Hole deviation from the table
- What it is
- Fundamental deviation of the hole read from the ISO limits table, with its sign.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts -10000 µm to 10000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Places the tolerance zone relative to the basic size.
- Get it right
- Read it in micrometres for the letter and the size step that contains the basic size.
What this means: Hole IT value from the table
- What it is
- Standard tolerance for the grade and size of the hole, from the IT table.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts 0.000001 µm to 10000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the width of the tolerance zone.
- Get it right
- Read it in micrometres, e.g. IT7 for 30 to 50 mm is 25 µm.
What this means: Delta value Δ for the hole (0 if none)
- What it is
- Delta value from the table for K, M and N holes to IT8 and P to ZC holes to IT7.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts 0 µm to 1000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Added to the tabulated upper deviation ES of the hole.
- Get it right
- Read it from the end of the hole deviation table; enter 0 for other holes.
What this means: Shaft deviation from the table
- What it is
- Which of the two shaft deviations the ISO table gives for the shaft letter.
- Units and format
- Choose one of 4 options from the list: Upper deviation es given (a to h); Lower deviation ei given (j to zc); h (es = 0); js (± IT ÷ 2).
- Example
- The form opens with “Lower deviation ei given (j to zc)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Decides how the other deviation is found.
- Get it right
- Shafts a to h have a tabulated es, j to zc a tabulated ei; choose h or js directly.
What this means: Shaft deviation from the table
- What it is
- Fundamental deviation of the shaft read from the ISO limits table, with its sign.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts -10000 µm to 10000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 26 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Places the tolerance zone relative to the basic size.
- Get it right
- Read it in micrometres for the letter and the size step that contains the basic size.
What this means: Shaft IT value from the table
- What it is
- Standard tolerance for the grade and size of the shaft, from the IT table.
- Units and format
- Enter a number in µm: micrometres (µm, microns). The form accepts 0.000001 µm to 10000 µm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 16 µm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the width of the tolerance zone.
- Get it right
- Read it in micrometres, e.g. IT7 for 30 to 50 mm is 25 µm.
Method and formulas
- Shaft: es given → ei = es − IT; ei given → es = ei + IT; h → es = 0, ei = −IT; js → ±IT ÷ 2.
- Hole: EI given → ES = EI + IT; ES given → ES = tabulated ES + Δ, then EI = ES − IT; H → EI = 0, ES = IT; Js → ±IT ÷ 2.
- Limits = basic size + deviation.
- Largest clearance = ES − ei; smallest clearance = EI − es; negative values are interference.
- Example: the hole is 45 to 45.025 mm and the shaft 45.026 to 45.042 mm.
Limitations
- The deviations, IT values and delta values come from the ISO limits tables for your size and grade and are entered by you.
- The tables cover sizes up to 3150 mm; check the size step the values are read from.
- Limits apply at 20 °C.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Turn a fit designation such as 45 H7/p6 into limits of size
- Apply the delta value for K, M, N and P to ZC holes
- See whether a fit is a clearance, transition or interference fit
Who it is for
- Design engineers
- Machinists
- Quality inspectors
What you get
- Upper and lower deviations of the hole and shaft
- Limits of size of the hole and shaft
- Largest and smallest clearance (negative = interference)
- Type of fit
Interpreting the result
- A positive smallest clearance is a clearance fit; a negative largest clearance is an interference fit; otherwise it is a transition fit.
- H holes and h shafts have their tolerance zones on the basic size, as in the hole-basis and shaft-basis systems.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 662–664. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Useful alongside · BIZOMAT original book
Limits and fits, recalculated from the drawings
In Checking Drawings by the Numbers
What it covers: Recalculate every fit from the limits on the two mating drawings, including the bore closure of a pressed bush, and find a running fit that can turn into an interference.
BIZOMAT 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 ISO Limits of Size and Fit from the Fundamental Deviations calculator