LO-6
Fixed and Floating Fasteners Formula
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6A Introduction to Fasteners
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Fastener
Nomenclature
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Fastener
Nomenclature
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Fastener
Nomenclature
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6B Floating Fasteners
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Floating Fasteners
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Floating Fastener Formulas
𝐻 =𝐹+𝑇
𝑇 =𝐻−𝐹
𝑇
𝐻
𝐹
Where
𝐻:
Minimum Diameter of Clearance
Hole (MMC Size of Hole)
𝐹:
Maximum Diameter of Fastener
(MMC Size of Fastener)
𝑇:
Positional Tolerance Diameter
(Diameter of the positional
tolerance zone
𝑇
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Example, Floating Fastener
Formulas

Given an application where an
M12X1.5 bolt is used to fasten two
identical parts with a hole diameter
of 13.0/12.5, the positional tolerance
required can be calculated as:

The MMC of a bolt is considered to
be the nominal size, which is the
same as the major diameter. The
major diameter of the M12Xl.5
thread is 12 mm.
𝑇 = 𝐻 − 𝐹 = 12.5 − 12 = 0.5
6C Fixed Fasteners
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Fixed Fasteners
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Fixed Fasteners
𝐻 = 𝐹 + 2𝑇
𝑇 = (𝐻 − 𝐹)/2
𝐻
𝐹
Where
𝐻:
Minimum Diameter of Clearance Hole (MMC Size of Hole)
𝐹:
Maximum Diameter of Fastener (MMC Size of Fastener
𝑇:
Positional Tolerance Diameter (Diameter of the positional
tolerance zone
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Example, Fixed Fasteners

Given an application where an M14X2
bolt is used to fasten two parts together,
where Part “A” has a clearance hole
diameter of 14.4/14.2 and Part “B” is
threaded with M14X2 thread to
accommodate the bolt, the positional
tolerance is calculated as follows:
𝐻 = 14.2
𝐹 = 14
𝐻−𝐹
14.2 − 14
𝑇=
=
= 0.1
2
2
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6D Fixed Fasteners with Unequal Positional Tolerance
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Fixed Fasteners with Unequal
Positional Tolerances
𝐻
𝐹
𝐻 = 𝐹 + 𝑇1 + 𝑇2
Fixed Fastener with Unequal
Positional Tolerance
𝐻 = 𝐹 + 2𝑇
Fixed Fastener with Equal Positional
Tolerance
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6D Additional Examples
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Additional Example, Floating
Fasteners
𝐹 = 10
𝐻 = 10.25
𝑇 =𝐻−𝐹
𝑇 = 10.25 − 10 = 0.25
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Additional Example, Floating
Fasteners
𝐹 = 10
𝑇 = 0.5
𝐻 =? ?
𝐻 =𝑇+𝐹
𝐻𝑀𝑀𝐶 = 0.5 + 10 = 10.5
𝐻𝑁𝑂𝑀 = 𝐻𝑀𝑀𝐶 + 0.25
𝐻𝑁𝑂𝑀 = 10.5 + 0.25 = 10.75
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Additional Example, Fixed
Fasteners
𝐹 = 10
𝑇 = 0.5
𝐻 =? ?
𝐻 = 2𝑇 + 𝐹
𝐻𝑀𝑀𝐶 = 2 × 0.8 + 10 = 11.6
𝐻𝑁𝑂𝑀 = 𝐻𝑀𝑀𝐶 + 0.25
𝐻𝑁𝑂𝑀 = 11.6 + 0.25 = 11.85
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End of LO5-C
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