BIZOMAT MAKEOS · Quality
Fastener Position Tolerance (Floating or Fixed) and Part Check
What position tolerance can I give the holes for these fasteners and clearance holes, and does a measured part pass with its bonus tolerance?
Position tolerance for a bolted pattern by the fastener formulas: floating fasteners (clearance holes in both parts) T = H − F, fixed fasteners (one part threaded or pressed) T₁ + T₂ = H − F split between the parts, with the projected tolerance zone reminder, then the check of a measured hole: actual position from the coordinate deviations, bonus tolerance from the departure from maximum material condition, and accept or reject (as the true position tool).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Fastener case | choice | Floating fasteners pass through clearance holes in all parts; fixed fasteners are held in one part (tapped hole, stud, dowel). |
| Clearance hole at MMC (smallest hole) | mm | Smallest permitted clearance hole (maximum material condition). |
| Fastener at MMC (largest fastener) | mm | Largest permitted fastener diameter. |
| Share of total tolerance given to the clearance-hole part (fixed case) | % | For fixed fasteners, the share of H − F given to the part with clearance holes (the rest goes to the threaded part, whose zone should be projected). |
| Measured hole | ||
| X deviation from true position | mm | Measured X offset of the hole from its true position. |
| Y deviation from true position | mm | Measured Y offset. |
| Measured hole size | mm | Measured size of that hole. |
| Hole size upper limit (LMC) | mm | Largest permitted size of the clearance hole. |
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: Fastener case
- What it is
- Floating means the fasteners pass through clearance holes in every part; fixed means one part holds the fastener in a tapped hole, stud or press fit.
- Units and format
- Choose one of 2 options from the list: Floating (clearance holes in both parts); Fixed (one part threaded or pressed).
- Example
- The form opens with “Floating (clearance holes in both parts)” selected as a worked example. Choose the option that matches your case.
- Get it right
- Fixed splits the H − F difference between the two parts using the share below.
What this means: Clearance hole at MMC (smallest hole)
- What it is
- The smallest size the clearance hole is allowed to be: its maximum material condition size.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 11 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Fastener at MMC (largest fastener)
- What it is
- The largest size the fastener is allowed to be: its maximum material condition size.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Share of total tolerance given to the clearance…
- What it is
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Ignored for floating fasteners, where each part gets the full H − F.
Measured hole
What this means: X deviation from true position
- What it is
- The measured X offset of the hole centre from its true (basic) position, from a CMM or layout measurement.
- Units and format
- Enter a number in mm: millimetres. The form accepts -100 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Y deviation from true position
- What it is
- The measured Y offset of the hole centre from its true position, at right angles to the X offset.
- Units and format
- Enter a number in mm: millimetres. The form accepts -100 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Position is 2√(Δx² + Δy²), a diameter, so enter the offsets as measured without doubling them.
What this means: Measured hole size
- What it is
- The measured actual diameter of the hole being checked; any amount above the MMC size adds bonus tolerance.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 11.1 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Hole size upper limit (LMC)
- What it is
- The largest permitted size of the clearance hole: its least material condition size.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 11.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Method and formulas
- Floating: T = H − F for each part; fixed: T₁ + T₂ = H − F, split by the share (project the threaded part’s zone).
- Actual position = 2√(Δx² + Δy²) (as the true position tool).
- Bonus at MMC = actual hole size − MMC size; allowed = T + bonus; accept if position ≤ allowed and the size is within limits.
- Example: the clearance holes get ⌀1 mm at MMC; the measured hole is at ⌀1 with ⌀1.1 allowed.
Limitations
- Zero-clearance assembly condition with no allowance for fastener head or thread tilt.
- Fixed-fastener zones should be projected by the mating part thickness.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set position tolerances for a bolted joint
- Check whether a part with off-position holes still assembles
- Choose clearance hole size for a positional tolerance
Who it is for
- Design engineers
- Inspectors
- Drafters
What you get
- Position tolerance at MMC for each part
- Actual position and bonus of the measured hole
- Accept or reject
Interpreting the result
- Bonus tolerance at MMC accepts parts with larger holes and more position error that still assemble.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 615–627. Topic reference; no source tables or recommended settings are reproduced.
- ASME Y14.5-2018 Dimensioning and Tolerancing
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Open the Fastener Position Tolerance (Floating or Fixed) and Part Check calculator