Spanner Sizes
What spanner size do I need?
If you find yourself asking, "What spanner size do I need for an M8 thread?" then look no further! Below, you will find a variety of thread sizes (metric) and the ideal spanner to tighten them. If you can't find the thread size you're looking for, let our Technical Team know through our Contact Us form.
Spanner sizes refer to the specific dimensions of spanners, which are hand tools used for tightening or loosening nuts and bolts. In Great Britain, spanners are usually measured in metric units (millimetres) or, in some cases, in imperial units (inches). The size of a spanner corresponds to the head size of the nut or bolt it fits. For instance, a 10mm spanner fits a nut with a head 10mm across. Spanners come in various types, such as open-end, ring, combination, and adjustable, each designed for specific tasks. The proper selection and use of a spanner size ensure a secure fit, preventing damage to the nut or bolt and ensuring safety during use.
Understanding the correct spanner size for a particular thread is crucial, especially in engineering, mechanical and construction work. This precise fit is necessary to avoid slippage, which can lead to rounded bolt heads or injury. It's essential to match the spanner size to the specific bolt head dimensions, as using an incorrect size can compromise the integrity of the bolt and the overall assembly. Each metric thread size has a corresponding spanner size, making it easier to select the right tool for the job without guesswork.
Additionally, using the right spanner size enhances efficiency and productivity. A well-fitted spanner allows for the application of appropriate torque, reducing the effort needed to tighten or loosen a bolt. This ensures a secure fit and prolongs the life of the spanner and the bolt. Investing in a quality set of spanners covering a range of standard sizes, including those for metric threads, can be invaluable for professional mechanics and DIY enthusiasts. Understanding and utilising the correct spanner sizes can lead to safer, more effective, and more efficient work.
Metric nut and bolt spanner sizes
| Thread Size | Spanner Size (mm) |
| M1.6 | 3.2 |
| M2 | 4 |
| M2.5 | 5 |
| M3 | 5.5 |
| M3.5 | 6 |
| M4 | 7 |
| M5 | 8 |
| M6 | 10 |
| M7 | 11 |
| M8 | 13 |
| M10 | 17 |
| M12 | 19 |
| M14 | 22 |
| M16 | 24 |
| M18 | 27 |
| M20 | 30 |
| M22 | 32 |
| M24 | 36 |
Inch (imperial) nuts and spanner sizes
Unlike metric measurements, imperial nut sizes are determined by the distance between the two parallel sides of the fastener, measured across flats (AF)
| Nut or bolt size across flats (inch) | Spanner Size (inch) |
| 1/4" | 7/16" |
| 5/16" | 1/2" |
| 3/8" | 9/16" |
| 7/16" | 5/8" |
| 1/2" | 3/4" |
| 9/16" | 7/8" |
| 5/8" | 15/16" |
| 3/4" | 1 1/8" |
| 1" | 1 1/2" |
