Bolts
Metric
The size of a metric fastener is determined by the outside diameter (OD) of the male threads. The length of a bolt is measured from the underneath of the head to the tip of the bolt. The wrench size used is based on the width between two opposite flats on the head of the bolt. The thread pitch is the distance between two adjacent peaks. All measurements are in millimeters (mm).
Common Metric Sizes
Although there are exceptions, common bolt sizes, thread pitches and wrench sizes are listed below.
| Bolt size | Pitch | Wrench size | Allen wrench | Torx wrench |
| 5 mm | .8 mm | 8 mm | 4 mm | T25 or T27 |
| 6 mm | 1.0 mm | 8 or 10 mm | 5 mm | T30 |
| 8 mm | 1.25 mm | 12 or 13 mm | 6 mm | T40 or T45 |
| 10 mm | 1.25 mm | 14 mm | 8 mm | T50 |
| 12 mm | 1.25 mm | 17 mm | 10 mm | T55 or T60 |
Standard (SAE)
The size of a standard fastener is determined by the outside diameter (OD) of the male threads. The length of a bolt is measured from the underneath of the head to the tip of the bolt. The wrench size used is based on the width between two opposite flats on the head of the bolt. The thread pitch is the number of threads per inch (tpi) and can be standard or fine thread. All measurements are in inches.
Although there are exceptions, common bolt sizes, thread pitches and wrench sizes are listed below.
| Bolt size | Standard pitch | Fine pitch | Wrench size |
| 1/4 in | 20 tpi | 28 tpi | 3/8 or 7/16 in |
| 5/16 in | 18 tpi | 24 tpi | 1/2 or 9/16 in |
| 3/8 in | 16 tpi | 24 tpi | 9/16 or 5/8 in |
| 7/16 in | 14 tpi | 20 tpi | 5/8 or 3/4 in |
| 1/2 in | 13 tpi | 20 tpi | 3/4 or 13/16 in |
| 9/16 in | 12 tpi | 18 tpi | 7/8 in |
| 5/8 in | 11 tpi | 18 tpi | 15/16 or 1 in |
| 3/4 in | 10 tpi | 16 tpi | 1 1/8 in |