If you're buying metric nuts for the first time — or you've been buying them for years but aren't sure exactly what you're getting — this guide covers everything you need to know. We'll explain the different types of metric nuts, what the grade and finish markings mean, and which nut is right for each application.
The standard hex full nut
The standard hex full nut (also called a hex head nut or full nut) is the most common metric nut used in construction, engineering, and fabrication. It has a regular hexagonal shape, is threaded all the way through, and is designed to be used with a bolt, set screw, or threaded rod of the same size and thread pitch.
Hex full nuts are manufactured to DIN 934 / ISO 4032 and are available in grade 8.8 steel in BZP, HDG, and A4 stainless finishes.
Understanding the size designation
Metric nuts are sized by their thread diameter — so an M10 nut fits an M10 bolt or threaded rod with a 1.5mm pitch. The nut's external dimensions are standardised, so an M10 nut from any manufacturer will have the same across-flats (A/F) dimension and can be tightened with the same spanner.
| Nut size | Thread pitch | A/F (spanner size) | Thickness |
|---|---|---|---|
| M6 | 1.0mm | 10mm | 5mm |
| M8 | 1.25mm | 13mm | 6.5mm |
| M10 | 1.5mm | 17mm | 8mm |
| M12 | 1.75mm | 19mm | 10mm |
| M16 | 2.0mm | 24mm | 13mm |
| M20 | 2.5mm | 30mm | 16mm |
| M24 | 3.0mm | 36mm | 19mm |
Types of metric nuts
Hex full nut (DIN 934)
The standard nut for most applications. Used with bolts, set screws, and threaded rod. Available in BZP, HDG, and A4 stainless.
Nyloc nut (DIN 985)
A standard hex nut with a nylon insert in the top section. When tightened, the nylon grips the bolt thread and resists loosening under vibration. Essential in automotive, machinery, and any dynamic application. Reusable, but the locking effect reduces slightly with each use.
Flange nut
A hex nut with a wide, built-in flange at the base that acts as an integrated washer. Eliminates the need for a separate washer in many applications and spreads the clamping load. Particularly useful for thin sheet metal and automotive applications.
Dome nut (DIN 1587)
Also called a cap nut or acorn nut. A hex nut with a closed, rounded top that covers the exposed end of the bolt or threaded rod. Used for cosmetic finish, thread protection, and to eliminate sharp protruding thread ends.
Grade 8.8 — what does it mean?
Nuts used with Grade 8.8 bolts and threaded rod are rated to match. The proof load strength of Grade 8.8 nuts means they can withstand the full clamping force of a Grade 8.8 bolt without stripping. Always use a nut rated to at least the same grade as the bolt or rod it's being used with.
Always match your finish
When assembling a fixing, use the same finish throughout. Don't mix BZP bolts with HDG nuts — in a wet environment, the galvanic potential difference between the two coatings can accelerate corrosion. BZP with BZP, HDG with HDG, A4 with A4.
