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Imperial vs Metric Bolt Sizes

Imperial vs Metric Bolt Sizes


Table Of Content


Imperial vs Metric Bolt Sizes

Feature Imperial Bolt Metric Bolt
Size 1/4", 1/2", 3/4", 1" M2, M3, M4, M5m M6
Measurement Inches, in MM, Pitch
Use Canada and USA Global, Asia, Europe
Standard Unified Thread Standard ISO Standard
Grades SAE Grade 5 Grade 8.8
Tensile Strength KSI or PSI MPa (Megapascals)
Threads Threads per Inch Pitch

What is Imperial Bolts?

What is Imperial Bolts?

  • Diameter: Imperial bolt is measured in inch.
  • Threads: UNEF, UNF, UNC.
  • Length: Imperial bolt is measured from the bottom head
  • Imperial bolts also called as the British imperial system

Imperial Bolt Size Chart

Thread Size Diameter Of Tapping Drill Diameter Of Pitch Threads Per Inch Major Diameter (inch)
5/16" 0.2770 0.2712" 18 TPI 0.3125
0.3480 0.3430" 24 TPI
0.3580 0.3537" 32 TPI
7/16" 0.3906 0.3850" 14 TPI 0.4375
0.4062 0.3995" 20 TPI
0.4130 0.4132" 28 TPI
3/4" 0.6875 0.6733" 10 TPI 0.7500
0.7031 0.7029" 16 TPI
0.7188 0.7162" 20 TPI
7/8" 0.7969 0.7946" 9 TPI 0.8750
0.8281 0.8216" 14 TPI
0.8438 0.8412" 20 TPI
1" 0.9219 0.9100 8 TPI 1.0000
0.9531 0.9382" 12 TPI
0.9688 0.9661" 20 TPI
1 1/4" 1.1093 1.1476 7 TPI 1.2500
1.1718 1.1879" 12 TPI
1 1/2" 1.3437 1.3812" 6 TPI 1.5000
1.4218 1.4376" 12 TPI
1 3/4" 1.5468 1.6085 5 TPI 1.7500
2" 1.7812 1.8528 4 1/2 TPI 2.0000
2 1/2" 2.1752 2.3345 4 TPI 2.5000
2 3/4" 2.4252 2.5844 4 TPI 2.7500
3" 2.6752 2.8344 4 TPI 3.0000
3 1/2" 3.1752 3.3343 4 TPI 3.5000
4" 3.6752 3.8342 4 TPI 4.0000

What is Metric Bolts?

What is Metric Bolts?

  • Diameter: Metric bolt is measured in metric system (millimeters).
  • Threads: coarse threads abd fine threads.
  • Length: Metric bolt is measured from the bottom of the head to the end.
  • Metric bolt based on the International System of Units (SI).

Metric Bolt Sizes

Thread Size Diameter Of Tapping Drill Diameter Of Pitch (mm) Thread Pitch (mm) Major Diameter
M64 58.00 mm 60.103 6.00 64.0 mm
M60 54.50 mm 56.428 5.50 60.0 mm
M56 50.50 mm 52.428 5.50 56.0 mm
M48 43.00 mm 44.752 5.00 48.0 mm
M45 40.50 mm 42.077 4.50 45.0 mm
M42 37.50 mm 39.077 4.50 42.0 mm
M39 35.00 mm 36.402 4.00 39.0 mm
M36 32.00 mm 33.402 4.00 36.0 mm
M33 29.50 mm 30.727 3.50 33.0 mm
M30 26.50 mm 27.727 3.50 30.0 mm
M27 24.00 mm 25.051 3.00 27.0 mm
M24 21.00 mm 22.051 3.00 24.0 mm
M22 19.50 mm 20.376 2.50 22.0 mm
M20 17.50 mm 18.376 2.50 20.0 mm
M18 15.50 mm 16.376 2.50 18.0 mm
M16 14.00 mm 14.701 2.00 16.0 mm
M14 12.00 mm 12.701 2.00 14.0 mm
M12 10.20 mm 10.863 1.75 12.0 mm
M11 9.50 mm 10.026 1.50 11.0 mm
M10 8.50 mm 9.026 1.50 10.0 mm
M9 7.80 mm 8.188 1.25 9.0 mm
M8 6.80 mm 7.188 1.25 8.0 mm
M7 6.00 mm 6.350 1.00 7.0 mm
M5 4.20 mm 4.480 0.80 5.0 mm
M4 3.30 mm 3.545 0.70 4.0 mm
M3 2.50 mm 2.675 0.50 3.0 mm
M2 1.60 mm 1.740 0.40 2.0 mm
M1 0.75 mm 0.838 0.25 1.0 mm

Complete Guide to Metric vs Imperial Screw Tensile Strength

Metric Bolt vs Imperial Bolt : Tensile Strength Comparison

Metric Bolt Imperial Bolt
Low Carbon Steel = 427 MPA Low Carbon Steel = 62,000 PSI
A80 Stainless Stainless 304 or 316 = 800 MPA A80 Stainless Stainless 304 or 316 = 116,000 PSI
Class 8.8 = 827 MPA SAE Grade 5 = 120,000 PSI
Class 10.9 = 1,034 MPA SAE Grade 8 = 150,000 PSI
High Tensile Class 12.9 (1,200 MPa) High Tensile 180,000 PSI

Check the Differences Between Imperial Fasteners vs. Metric Fasteners Threads


Imperial & Metric Thread Identification

Imperial & Metric Thread Identification

Designations Of Imperial Bolt and Metric Bolt

Designations Of Imperial Bolt and Metric Bolt

How Are The Metric And Imperial Systems Marked?

  • Metric thread starts with the M, Example: M12 (O.D. of 12mm)
  • Imperial is normally marked with W*N, Example: 1/4"-20×3"

Metric and Imperial Bolt Sizes Explained

Imperial Bolt Metric Bolt
Imperial bolts are measured in inches Metric bolts are measured in mm (millimetres)
Imperial bolt following imperial system Metric bolt is start with the letter "M"
1/4" means a diameter of bolt (1/4 inch) M6 means a diameter of bolt (6mm)

Know More About Imperial Bolt vs Metric Bolt Torque Chart


Imperial Bolt Torque Chart

Size Recommended Imperial Bolt Torque (lb-ft)
SAE Grade 8 SAE Grade 5
Coarse Fine Coarse Fine
1" 682 764 483 541
7/8" 454 501 322 355
3/4" 282 315 200 223
5/8" 150 180 112 128
9/16" 115 129 82 91
1/2" 80 90 57 64
7/16" 52 58 37 41
3/8" 33 37 23 26
5/16" 18 20 13 14
1/4" 9 10 6.3 7.3

Metric Bolt Torque Chart

Size Recommended Imperial Bolt Torque (Nm)
Grade 12.9 Grade 10.9 Grade 8.8
M30 2774 2377 1719
M24 1395 1195 865
M20 809 690 500
M16 413 354 248
M12 167 143 99.8
M10 95.7 81.8 57.3
M8 48.3 41.3 28.8
M6 19.9 17.0 11.8
M5 11.7 10.0 7.0

Metric vs Imperial: Which System Should You Use?

Metric Bolt Imperial Bolt
Strength by numbers Grade by letter
mm Threads per inch
measured in mm measured in inch

How to Measure Metric Bolt Size?

  • View the thread pitch
  • Length measure
  • Diameter measure

How to Use Imperial To Metric Fasteners Conversion Table?

  • Ensure right size selection
  • Check the closest imperial equivalent
  • Identify the metric fastener size
Refer Metric vs Imperial Bolt Grades Comparison

Imperial Bolt Grades

Imperial bolt suitable for grade 2, grade 5, grade 8.

Metric Bolt Grades

Metric bolt suitable for grade 4.6, grade 8.8, grade 10.9, grade 12.9.

Imperial Bolt Threads and Spanner Sizes

Shaft Diameter UNF threads per inch BSF threads per inch UNF spanner size BSF spanner size
1" 12 10 1" 1/2" 1" 15/32"
3/4" 16 12 1" 1/8" 1" 3/16"
5/8" 18 14 15/16" 1"
9/16" 18 16 7/8" 59/64"
1/2" 20 16 3/4" 13/16"
7/16" 20 18 5/8" 45/64"
3/8" 24 20 9/16" 19/32"
5/16" 24 22 1/2" 17/32"
1/4" 28 26 7/16" 7/16"

Imperial Bolt Thread Lengths

Diameter of Imperial Bolts Longer Than 6" 6" and Shorter
4" 8.5" 8.25"
3" 3/4" 8" 7.75"
3" 1/4" 7" 6.75"
3" 6.5" 6.25"
2" 1/2" 5.5" 5.25"
2" 4.5" 4.25"
1" 3/4" 4" 3.75"
1" 1/2" 3.5" 3.25"
1" 3/8" 3.25" 3"
1" 1/8" 2.75" 2.5"
1" 2.5" 2.25"
3/4" 2" 1.75"
5/8" 1.75" 1.5"
1/2" 1.5" 1.25"
3/8" 1.25" 1"
1/4" 1" 0.75"

Metric Vs Imperial Screw Sizes

Imperial Screw Metric Screw
Nominal Size (Gauge) Length Diameter (mm) Length
12 3 1/2" 6 90 mm
12 3" 6 80 mm
12 2 1/2" 6 60 mm
12 2" 6 50 mm
10 4" 5 100 mm
10 3 1/2" 5 90 mm
10 3" 5 80 mm
10 2" 5 50 mm
10 1 1/4" 5 30 mm
8 2 3/4" 4 70 mm
8 2 1/2" 4 60 mm
8 2" 4 50 mm
8 1 1/2" 4 40 mm
8 1 1/2" 4 40 mm
8 3/4" 4 20 mm
6 1 1/4" 3.5 30 mm
6 3/4" 3.5 20 mm
6 1/2" 3.5 12 mm
4 1" 3 25 mm
4 1/2" 3 12 mm

Metric Bolt Thread

Metric bolt expressed by thread pitch.

Metric Bolt Thread

Imperial Bolt Threads

Imperial bolt expressed by thread count.

Imperial Bolt Threads

Metric and Imperial Equivalents

Metric (Pitch in mm) British Standard (Threads Per Inch)
Size Fine Coarse (mm) Size Fine (BSF Threads) Coarse (BSW Threads)
M60 4.00 mm 5.50   - -
M58 4.00 mm -   - -
M56 4.00 mm 5.50 2 ¼" 6 4
M55 4.00 mm -   - -
M52 4.00 mm 5.00 2” 7 4.5
M50 3.00 mm -   - -
M48 4.00 mm 5.00   - -
M42 4.00 mm 4.50   - -
M40 3.00 mm -   - -
M38 1.50 mm -   - -
M36 3.00 mm 4.00 1 ½" 8 6
M32 2.00 mm 00   - -
M30 2.00 mm 3.50 1 ¼" 9 7
M28 2.00 mm -   - -
M24 2.00 mm 3.00 1" 10 8
M22 1.50 mm 2.50 7/8” 11 9
M20 1.50 mm - 3/4" 12 10
M18 1.50 mm 2.50   - -
M16 1.50 mm 2.00 5/8” 14 11
M14 1.50 mm 2.00 9/16" 16 12
M12 1.25 mm 1.75 1/2" 16 12
M10 1.25 mm 1.50 3/8" 20 16
M8 1.00 mm 1.25 5/16" 22 18
M6 0.75 mm 1.00 0BA - -
M4 0.50 mm 0.70 3BA - -

Metric Bolts Hole Sizes

Size Clearance Hole Fine Pitch Tapping Drill (mm) Fine Thread Pitch STD Thread Pitch Fine Thread Pitch
M30 32 mm 28 2.0 3.5 2.0
M24 26 mm 22 2.0 3.0 2.0
M20 22 mm 20.5 1.5 2.5 1.5
M16 18 mm 16.5 1.5 2.0 1.5
M12 14 mm 10.5 1.5 1.75 1.5
M10 11 mm 9.0 or 8.75 1.0 or 1.25 1.5 1.0 or 1.25
M8 9 mm 7 1.0 1.25 1.0
M6 6.5 mm 5.25 0.75 1.0 0.75
M5 5.5 mm - - 0.8 -