5/16-18 Bolt Size and Thread Specifications
5/16-18 is a common imperial (UNC) bolt size. A 5/16 inch nominal diameter with 18 threads per inch is used in automotive, machinery, and structural applications in North America.
Specifications
| Specification | Value |
|---|---|
| Nominal diameter | 0.3125 in (7.94 mm) |
| Threads per inch (TPI) | 18 |
| Tap drill size | F (0.257 in) |
| Closest metric equivalent | M8 |
Hex head size
| Bolt size | Hex head size |
|---|---|
| 5/16-18 | 1/2 in |
Common uses
5/16-18 bolts are used in automotive, machinery, and structural connections. They are a standard size between 1/4-20 and 3/8-16 and are widely stocked.
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FAQ
What does 5/16-18 mean?
5/16 is the nominal diameter in inches (0.3125 in). 18 is the number of threads per inch (TPI). It is a common UNC coarse thread.
What drill size for 5/16-18 tap?
Use an F drill (0.257 in) for a standard 5/16-18 tap.
What metric bolt is closest to 5/16-18?
M8 is the closest metric equivalent to 5/16-18. See M8 bolt size for full specs.