Have you ever stood bewildered in front of hardware store shelves, overwhelmed by the array of screw and bolt sizes? The confusing mix of numbering systems, fractional inches, and metric measurements can stall even the most straightforward projects. This comprehensive guide will demystify American fastener sizing and provide the tools you need for flawless project execution.
Chapter 1: Decoding American Screw Sizes
Unlike the metric system's straightforward millimeter measurements, American screws use a numbering system (#0 through #14) that corresponds to specific diameters. Our conversion chart eliminates the guesswork:
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Screw Size
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Decimal Inches
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Approximate Fraction
|
Metric Equivalent (mm)
|
Common Applications
|
|
#0
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0.060 in.
|
1/16"
|
1.52 mm
|
Eyeglasses, precision instruments
|
|
#6
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0.138 in.
|
9/64"
|
3.51 mm
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Wood screws, metal connections
|
|
#10
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0.190 in.
|
3/16"
|
4.83 mm
|
Heavy furniture, automotive interiors
|
|
#14
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0.250 in.
|
1/4"
|
6.35 mm
|
Heavy machinery, structural applications
|
Practical Application:
When selecting a screw for wood paneling requiring approximately 4mm diameter, our chart shows #8 screws (4.17mm) provide the closest match. Always verify with calipers for precision.
Chapter 2: Bolt Diameter Conversion
For bolts larger than #14, diameters are expressed in fractional inches. Our conversion chart simplifies inch-to-metric translation:
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Bolt Diameter
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Decimal Inches
|
Metric Equivalent (mm)
|
|
1/4"
|
0.250
|
6.35 mm
|
|
1/2"
|
0.500
|
12.70 mm
|
|
1"
|
1.000
|
25.40 mm
|
Selection Considerations:
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Match strength grades to load requirements
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Consider thread type (coarse vs fine)
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Account for material compatibility
Chapter 3: Fractional Inch to Metric Conversion
This comprehensive reference enables seamless transitions between measurement systems:
|
Fractional Inch
|
Metric (mm)
|
Fractional Inch
|
Metric (mm)
|
|
1/8"
|
3.18 mm
|
1-1/2"
|
38.10 mm
|
|
1/4"
|
6.35 mm
|
2"
|
50.80 mm
|
Chapter 4: Frequently Asked Questions
Why do different sizing standards exist?
Historical industrial development created regional standards - primarily imperial in the U.S. and metric elsewhere.
How to measure fastener dimensions accurately?
Use digital calipers to measure:
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Diameter: Thread crest-to-crest
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Length: Underside of head to tip
What determines load capacity?
Key factors include:
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Diameter (larger = stronger)
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Material composition
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Thread configuration
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Strength grade markings
Outdoor fastener considerations:
Select corrosion-resistant materials:
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Stainless steel (all-purpose)
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Brass (marine environments)
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Coated steel (general outdoor use)
Chapter 5: Key Takeaways
Proper fastener selection ensures project integrity and safety. Remember:
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Understand American sizing conventions
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Use conversion charts for accuracy
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Match hole sizes appropriately
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Consider environmental factors
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Verify measurements with precision tools
With this reference guide, fastener selection becomes a precise science rather than a frustrating obstacle. Whether undertaking DIY projects, repairs, or construction work, these tools will help achieve professional results consistently.
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