# Fixed and Floating Fastener Position Tolerance Calculator

> Source: https://netray.co/tools/fixed-and-floating-fastener-position-tolerance-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Calculate the position tolerance for clearance holes using the floating and fixed fastener formulas, split it between parts and check the hole at LMC.

## Category

engineering-plm

## Industry

Contract Manufacturing

## Audience

- Design engineer
- Manufacturing engineer
- Quality engineer

## Tool

**Kind:** calculator

**Inputs:**

#### Clearance hole at MMC (smallest diameter)

**Key:** hole_mmc

**Type:** number

**Default:** 9

**Min:** 0.1

**Step:** 0.01

**Unit:** mm

#### Fastener at MMC (largest diameter)

**Key:** fastener_max

**Type:** number

**Default:** 7.972

**Min:** 0.1

**Step:** 0.001

**Unit:** mm

**Help:** Use the maximum shank or major diameter, for example 7.972 for an M8 6g bolt.

#### Hole size tolerance (MMC to LMC)

**Key:** hole_size_tol

**Type:** number

**Default:** 0.15

**Min:** 0

**Step:** 0.01

**Unit:** mm

#### Share of tolerance allocated to part 1 (fixed case)

**Key:** alloc_pct

**Type:** slider

**Default:** 50

**Min:** 10

**Max:** 90

**Step:** 5

**Unit:** %

#### Reserve for fastener tilt or form

**Key:** reserve_pct

**Type:** slider

**Default:** 10

**Min:** 0

**Max:** 40

**Step:** 5

**Unit:** %

**Help:** Unallocated tolerance kept in hand for perpendicularity or thread error.

**Outputs:**

#### Diametral clearance (H - F)

**Key:** clearance

**Expr:** hole_mmc - fastener_max

**Format:** decimal

#### Floating fastener position tolerance (T = H - F)

**Key:** float_t

**Expr:** hole_mmc - fastener_max

**Format:** decimal

**Primary:** true

**Description:** Applies to each of the parts when all clearance holes are in separate parts and the fastener floats in all of them.

#### Floating, after reserve

**Key:** float_use

**Expr:** float_t * (1 - reserve_pct / 100)

**Format:** decimal

#### Fixed fastener total, both parts (T1 + T2 = H - F)

**Key:** fixed_total

**Expr:** hole_mmc - fastener_max

**Format:** decimal

**Description:** Total tolerance for threaded or press-fit part plus clearance part.

#### Fixed fastener, equal split per part ((H - F) / 2)

**Key:** fixed_equal

**Expr:** (hole_mmc - fastener_max) / 2

**Format:** decimal

**Primary:** true

#### Part 1 tolerance at selected allocation, after reserve

**Key:** part1

**Expr:** fixed_total * alloc_pct / 100 * (1 - reserve_pct / 100)

**Format:** decimal

#### Part 2 tolerance at selected allocation, after reserve

**Key:** part2

**Expr:** fixed_total * (100 - alloc_pct) / 100 * (1 - reserve_pct / 100)

**Format:** decimal

#### Clearance hole at LMC (largest diameter)

**Key:** hole_lmc

**Expr:** hole_mmc + hole_size_tol

**Format:** decimal

#### Floating position allowed with the hole at LMC (T + size departure)

**Key:** float_lmc

**Expr:** float_t + hole_size_tol

**Format:** decimal

**Description:** Under MMC, the hole at its largest size adds the full size tolerance as bonus.

**Chart:**

#### Fastener position tolerance versus clearance hole size

**Type:** line

**X:** hole_mmc

**From:** 8.4

**To:** 10.4

**Steps:** 21

**Series:**

- float_t
- fixed_equal
- float_use

**Disclaimer:** These are the standard ASME Y14.5 fixed and floating fastener formulas for position at MMC. They assume the fastener does not bend, the holes are perpendicular to their mating faces, and the position tolerance is applied at MMC. Use a projected tolerance zone for threaded holes and verify against your drawing standard.

## Content

**Intro:** The floating and fixed fastener formulas tell you how much position tolerance a pattern of clearance holes can have while guaranteeing a bolt still fits. They are among the most common calculations in GD&T, and this calculator gives both cases and a safe reserve.

**Sections:**

#### How to use it

**Body:** Enter the clearance hole at MMC, meaning its smallest allowed diameter, and the fastener at MMC, meaning the largest shank or major diameter. Choose how much tolerance to reserve for fastener tilt and thread error, and how to split the fixed case between the two parts. The results give the floating tolerance, the fixed total and equal split, the allocation after reserve, and the position allowed when the hole is at its largest size. Use the chart to see how stepping up the clearance hole size, for example from fine to medium series, multiplies the tolerance you can give.

**Bullets:**

- Floating: the fastener passes through clearance holes in all parts, such as a bolt and nut.
- Fixed: the fastener is held in one part, such as a tapped hole, stud or press-fit pin.
- Always use MMC sizes in both formulas.
- Apply the resulting tolerance at MMC in the feature control frame.

#### The formulas

**Body:** For a floating fastener, T = H - F, where H is the clearance hole at MMC and F is the fastener at MMC. The fastener floats, so each hole may use the entire clearance. For a fixed fastener, T = (H - F) / 2: the tolerance is split between the part with the clearance hole and the part holding the fastener, because their errors add. The total of both parts is H - F, and the split can be unequal if one process is more capable. These formulas give zero-interference at worst case, where both holes are at MMC and the fastener is at its maximum.

#### Worked example

**Body:** An M8 bolt has a maximum major diameter of 7.972 mm for a 6g thread. The medium-series clearance hole of 9.000 mm gives a diametral clearance of 1.028 mm, so a floating pattern can use a position tolerance of 1.028 mm at MMC. If the bolt threads into a tapped part, the total of 1.028 mm is shared, so an equal split gives 0.514 mm to each. After a 10 percent reserve, the floating tolerance is about 0.925 mm. If the clearance hole is made to a tighter 8.400 mm fine-series size, the floating tolerance falls to 0.428 mm.

#### Common mistakes

**Body:** Using the nominal fastener size rather than the maximum shank diameter overstates the tolerance. Using the largest hole size rather than the MMC hole size does the same. Forgetting the projected tolerance zone on tapped or press-fit holes ignores the fastener tilt over the mating length, which can make a pattern that passes inspection fail at assembly. Finally, applying the floating formula where one part has a threaded hole is unsafe, since that part cannot float: use the fixed formula for it.

**Cta:** If you want hole patterns and fastener data checked automatically against drawing callouts, Netray can help build a private assistant on top of your PLM or ERP part data.

**Faq:**

#### When is a fastener floating and when is it fixed?

**Answer:** It is floating when the fastener passes through clearance holes in every part, such as a bolt and nut through two plates. It is fixed when it is restrained in one of the parts, such as a screw into a tapped hole, a stud or a press-fit pin.

#### Why divide by two for fixed fasteners?

**Answer:** Because the position errors of the two parts add up. If part 1 is off by T1 and part 2 by T2, the holes still align when T1 + T2 is less than the clearance H - F. An equal split gives each part half. An unequal split is fine if the total does not exceed H - F.

#### Should I use MMC or RFS?

**Answer:** The formulas assume the position tolerance is applied at MMC, so the tolerance can grow as the hole departs from MMC. With RFS the formula values are still the minimum safe value, but you lose the bonus, so MMC usually gives better manufacturability.

#### What about a threaded hole?

**Answer:** Use the fixed formula, and add a projected tolerance zone equal to the thickness of the mating part, so the tolerance applies at the fastener location rather than inside the hole. Without the projection, a tilted thread can pass inspection but still block assembly.

## Search terms

floating fastener formula, fixed fastener formula gd&t, position tolerance for clearance hole calculator, gd&t fastener tolerance, hole minus fastener position tolerance, clearance hole position tolerance bolt, asme y14.5 fastener formula

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