Bolt Size Chart: Metric and SAE Conversions (Complete Reference)
Overview
Whether you're a professional mechanic, automotive enthusiast, or weekend DIYer, having a comprehensive bolt size chart at your fingertips saves time and prevents costly mistakes. This reference covers metric and SAE bolt sizes, conversions, and thread specifications for fasteners from 1mm to 1 inch and beyond.
How to Read Bolt Sizes
A bolt size designation contains three key pieces of information:
Example: M10x1.5 x 50mm
│ │ │
│ │ └── Length (50mm)
│ └─────── Thread pitch (1.5mm between threads)
└─────────── Diameter (10mm)
Example: 3/8"-16 x 2"
│ │ │
│ │ └── Length (2 inches)
│ └─────── Threads per inch (16 TPI)
└──────────── Diameter (3/8 inch)
Complete Metric Bolt Size Chart
Small Metric Bolts (M1 - M5)
Size
Thread Pitch (mm)
Lengths Available (mm)
TPI Equivalent
M1
0.25
6, 8, 10
~100 TPI
M1.2
0.25
6, 8, 10
~100 TPI
M1.4
0.3
6, 8, 10
~84 TPI
M1.6
0.35
8, 10, 12
~72 TPI
M2
0.4
8, 10, 12, 16
~64 TPI
M2.5
0.45
10, 12, 16, 20
~56 TPI
M3
0.5
10, 12, 16, 20, 25
~50 TPI
M3.5
0.6
10, 16, 20, 25
~42 TPI
M4
0.7
12, 16, 20, 25, 30
~36 TPI
M5
0.8
16, 20, 25, 30, 40
~32 TPI
Medium Metric Bolts (M6 - M12)
Size
Thread Pitch (mm)
Lengths Available (mm)
Nearest SAE
M6
1.0
16, 20, 25, 30, 40, 50
1/4"
M8
1.25
20, 25, 30, 40, 50, 60
5/16"
M10
1.5
25, 30, 35, 40, 50, 60
3/8"
M12
1.75
30, 35, 40, 50, 60, 80
7/16"
Large Metric Bolts (M14 - M24)
Size
Thread Pitch (mm)
Lengths Available (mm)
Nearest SAE
M14
2.0
30, 40, 50, 60, 80, 100
9/16"
M16
2.0
40, 50, 60, 80, 100
5/8"
M18
2.5
50, 60, 80, 100
3/4"
M20
2.5
50, 60, 80, 100, 120
3/4"
M22
2.5
60, 80, 100, 120
7/8"
M24
3.0
60, 80, 100, 120, 150
1"
Extra-Large Metric Bolts (M27 - M39)
Size
Thread Pitch (mm)
Lengths Available (mm)
M27
3.0
80, 100, 120
M30
3.5
80, 100, 120, 150
M33
3.5
100, 120, 150
M36
4.0
100, 120, 150, 200
M39
4.0
120, 150, 200
Complete SAE Bolt Size Chart
Small SAE Bolts
Size
TPI (UNC)
TPI (UNF)
Lengths Available (")
#0
80
—
1/8, 3/16, 1/4
#1
64
—
1/4, 5/16
#2
56
—
1/4, 5/16, 3/8
#3
48
—
1/4, 5/16, 3/8
#4
40
48
3/8, 7/16, 1/2
#5
40
44
3/8, 7/16, 1/2
#6
32
40
1/2, 5/8, 3/4
#8
32
36
5/8, 3/4, 7/8
#10
24
32
3/4, 7/8, 1"
Medium SAE Bolts
Size
TPI (UNC)
TPI (UNF)
Lengths Available (")
1/4"
20
28
1/2 to 4"
5/16"
18
24
1/2 to 6"
3/8"
16
24
3/4 to 8"
7/16"
14
20
1/2 to 6"
1/2"
13
20
3/4 to 12"
9/16"
12
18
3/4 to 12"
5/8"
11
18
1 to 14"
3/4"
10
16
1 to 16"
Large SAE Bolts
Size
TPI (UNC)
TPI (UNF)
Lengths Available (")
7/8"
9
14
1 to 18"
1"
8
12
1-1/4 to 24"
1-1/8"
7
12
1-1/2 to 24"
1-1/4"
7
12
1-1/2 to 24"
1-3/8"
6
12
2 to 24"
1-1/2"
6
12
2 to 24"
SAE to Metric Conversion Chart
Most Common Automotive Sizes
SAE Size
Metric Equivalent
Difference
1/4"
M6 (6mm)
0.014" (close fit for wrenches)
5/16"
M8 (8mm)
0.013"
3/8"
M10 (10mm)
0.025"
7/16"
M12 (12mm)
0.013"
1/2"
M14 (14mm)
0.025"
9/16"
M16 (16mm)
0.014"
5/8"
M18 (18mm)
0.018"
3/4"
M20 (20mm)
0.022"
Fraction-to-Decimal Reference
Fraction
Decimal
Millimeters
1/16"
0.0625"
1.59mm
1/8"
0.125"
3.18mm
3/16"
0.1875"
4.76mm
1/4"
0.250"
6.35mm
5/16"
0.3125"
7.94mm
3/8"
0.375"
9.53mm
7/16"
0.4375"
11.11mm
1/2"
0.500"
12.70mm
9/16"
0.5625"
14.29mm
5/8"
0.625"
15.88mm
11/16"
0.6875"
17.46mm
3/4"
0.750"
19.05mm
13/16"
0.8125"
20.64mm
7/8"
0.875"
22.23mm
15/16"
0.9375"
23.81mm
1"
1.000"
25.40mm
Thread Pitch Comparison Chart
Metric Coarse vs. Fine Pitch
Diameter
Coarse Pitch
Fine Pitch
Extra Fine
M5
0.8
0.5
—
M6
1.0
0.75
—
M8
1.25
1.0
—
M10
1.5
1.25
1.0
M12
1.75
1.5
1.25
M14
2.0
1.5
—
M16
2.0
1.5
1.0
M18
2.5
2.0
1.5
M20
2.5
2.0
1.5
M24
3.0
2.0
1.5
SAE Coarse vs. Fine Pitch
Diameter
UNC
UNF
UNEF
1/4"
20
28
—
5/16"
18
24
—
3/8"
16
24
32
1/2"
13
20
28
5/8"
11
18
—
3/4"
10
16
—
Common Automotive Applications
Engine Fasteners
Component
Typical Size
Thread Pitch
Torque Range
Head bolts
M10-M12
1.5-1.75mm
60-90 ft-lbs
Main cap bolts
M12-M14
1.75-2.0mm
80-120 ft-lbs
Connecting rod bolts
M10-M12
1.25-1.5mm
50-80 ft-lbs
Oil pan bolts
M6-M8
1.0-1.25mm
15-25 ft-lbs
Valve cover bolts
M6-M8
1.0-1.25mm
10-20 ft-lbs
Spark plugs
M12-M14
1.25-1.5mm
15-25 ft-lbs
Suspension & Chassis
Component
Typical Size
Thread Pitch
Torque Range
Control arm bolts
M12-M16
1.5-2.0mm
80-130 ft-lbs
Sway bar links
M8-M12
1.25-1.75mm
25-55 ft-lbs
Strut bolts
M12-M14
1.5-2.0mm
70-100 ft-lbs
Tie rod ends
M12-M16
1.5-2.0mm
40-80 ft-lbs
Brake System
Component
Typical Size
Thread Pitch
Torque Range
Caliper bolts
M8-M12
1.25-1.75mm
25-65 ft-lbs
Caliper bracket bolts
M10-M14
1.25-2.0mm
50-90 ft-lbs
Rotor hat bolts
M8-M10
1.25-1.5mm
20-40 ft-lbs
Wheels
Component
Typical Size
Thread Pitch
Torque Range
Lug nuts/bolts (compact)
M10-M12
1.25-1.5mm
70-90 ft-lbs
Lug nuts/bolts (truck/SUV)
M14-M16
1.5-2.0mm
100-160 ft-lbs
Quick-Reference: SAE Wrench Size to Bolt Size
Wrench Size
Bolt Size
5/16"
1/4"-8
3/8"
5/16"-18, 10mm
7/16"
3/8"-16
1/2"
7/16"-14, 10mm-1.5
9/16"
1/2"-13
5/8"
9/16"-12
11/16"
5/8"-11
3/4"
3/4"-10
13/16"
7/8"-9
15/16"
1"-8
1-1/16"
1-1/8"-7
1-1/4"
1-1/4"-7
1-5/16"
1-3/8"-6
How to Print This Chart
This chart is designed to be printed and kept in your garage or toolbox. For best results:
Related Articles
Tags
#bolt-size-chart #metric-to-sae #bolt-conversion #fastener-reference #automotive-repair #bolt-sizes
Tools for measuring a bolt you can’t identify A size chart only helps once you know the thread pitch and the diameter — these two measure both.
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Recommended Tool · read the pitch off the thread
Thread pitch gauge (metric + SAE) Leaves are stamped in both mm pitch and threads-per-inch, so one tool settles whether you’re holding an M10×1.5 or a 3/8"-16. Guessing pitch by eye is how cross-threading starts.
Recommended Tool · measure the shank, not the head
Digital caliper (6 in / 150 mm) Bolt diameter is measured across the thread crests, and the difference between M8 and 5/16" is under half a millimetre — too close to eyeball. Switches between inch, metric and fractions.
