Standard to Metric bolt conversions.
Not proud but I did swipe this from Elgin Fasteners. I’ve read that the holes in the Subaru WRX STi (VAB) front bumper are #10 and to use #10 well nuts. But what if I wanted metric sized well nuts, you know, like everything else on the car, planet, etc? Well, here’s a table to help out in your quest.
Now onto Dress Up Bolts or ZSpec Design for some fancy!
Metric Bolt Conversion
Metric bolt conversion data for industrial bolts/rods, machine screws and small diameter fasteners from Elgin Fastener Group includes metric to standard bolt conversions. The chart below shows metric bolt conversions and DIN numbers for fasteners.
Fastener Conversion | Approximate Equivalency | Common DIN Numbers
Diameter/Decimal/Metric Chart for Small Diameter Fasteners
| Gauge or Diameter |
Decimal (in) | mm |  |
| No.0000 | 0.021 | .53 | |
| No.000 | 0.034 | .86 | |
| No.00 | 0.047 | 1.19 | |
| No.0 | 0.060 | 1.524 | |
| No.1 | 0.073 | 1.854 | |
| No.2 | 0.086 | 2.184 | |
| No.3 | 0.099 | 2.515 | |
| No.4 | 0.112 | 2.845 | |
| No.5 | 0.125 | 3.175 | |
| No.6 | 0.138 | 3.505 | |
| No.8 | 0.164 | 4.166 | |
| No.10 | 0.190 | 4.826 | |
| No.12 | 0.216 | 5.484 |
Fastener Conversion Chart
| Inch Equivalent | Metric Size-PitchISO and IFI Rec. | |
| UNC | UNF | |
| 1- 64 | 1- 72 | M2x 0.4 |
| 3- 48 | 3- 56 | M2.5x 0.45 |
| 4- 40 | 4- 48 | M3x .5 |
| 6- 32 | 6- 40 | M3.5x .6 |
| 8- 32 | 8- 36 | M4x .7 |
| 10- 24 | 10- 32 | M5x .8 |
| 1/4- 20 | 1/4- 28 | M6x 1 |
| 5/16-18 | 5/16- 24 | M8x 1.25 |
| 3/8-16 | 3/8- 24 | M10x 1.5 |
| 7/16-14 | 7/16- 20 | M12x 1.75 |
| 1/2- 13 | 1/2- 20 | M14x 2 |
| 5/8- 11 | 5/8- 18 | M18x 2 |
| 3/4- 10 | 3/4- 16 | M20x 2.5 |
| 1- 8 | 1-12 | M24x 3 |
| 1-1/4- 7 | 1-1/8- 12 | M30x 3.5 |
| 1-1/2- 6 | 1-1/4- 12 | M36x 4 |
Approximate Equivalency Chart Metric/US Roughly Equivalent US Bolt Materials
| Metric Nut Class | SAE J429Normally Used | Grades | ASTM Grades |
| 4.6 | 4or 5 | 1 | A307,Grade A |
| 4.8 | 4or 5 | 2 | . |
| 5.8 | 5 | 2 | . |
| 8.8 | 8 | 5 | A325,A449 |
| 9.8 | 9 | 5+ | A193,B7 and B16 |
| 10.9 | 10or 12 | 8 | A490,A354, Grade 8D |
| 12.9 | 10or 12 | . | A540;B21 through B24 |
Common DIN Numbers for Metric Fasteners
| DIN | Hex Capscrews | ||
| 931 | Coarse thread pitch partially threaded (specify grade) | ||
| 933 | Coarse thread pitch fully threaded (specify grade) | ||
| 930 | Fine thread pitch partially threaded (specify grade) | ||
| 961 | Fine thread pitch fully threaded (specify grade) | ||
| DIN | Nuts | ||
| 934 | Hex nuts (specify pitch and class) | ||
| 985 | Nylon insert locknuts (specify pitch and class) | ||
| 980V | All metal locknuts (specify pitch and class) | ||
| DIN | Washers | ||
| 125 | Flatwashers | ||
| 127 | Lockwashers | ||
| DIN | Socket Products | ||
| 912 | Socket head capscrews (normally GR 12.9 and coarse thread) | ||
| 7991 | Flat head socket capscrews (normally GR 12.9 and coarse thread) | ||
| 916 | Socket setscrews (normally GR 12.9 and coarse thread) | ||
| DIN | Machine Screws | ||
| 7985 | Pan head Phillips drive zinc plated | ||
| 965 | Flat head Phillips drive zinc plated | ||
| DIN | Threaded Rod | ||
| 975 | All threaded rod (normally 1 meter lengths, specify grade and pitch) | ||