How to choose nuts: thread, material and the right type
The right nut has the same thread as the screw or rod (from M3 to M30 in the collection) and the same material: galvanised with galvanised, stainless with stainless. Then choose the type according to the job: hex for normal fastening, self-locking nut or lock nut where there is vibration, dome nut to protect the end of the screw, wing nut for tightening and loosening by hand. A nut with the wrong thread or material will not hold, or will be ruined in no time.
The types
- Hex nut: the general-purpose nut, tightened with a spanner or socket. You will find them in galvanised steel, stainless steel and brass.
- Self-locking nut: has a system that stops it undoing by itself under vibration; usually with a nylon ring that grips the thread.
- Flange nut: has a flange at the base that spreads the load, so a washer is often not needed.
- Dome nut: closed at one end, it covers the end of the screw, protects the thread and makes the head tidier and less sharp.
- Wing nut: has two wings so it can be tightened by hand, without tools. Used where frequent dismantling is needed.
- Lock nuts and safety nuts: fitted as a pair with another nut to lock it.
- Hex coupling nut: joins two threaded rods in line. One example is the RD coupling nut Fischer.
- Nuts for specific systems: such as the FCN Clix S hammer-head nut or the quick-fit nut of the Clix series. They belong to a specific fastening system and are chosen from the product page of that system, not as a generic nut.
How to choose by job
| Job | Recommended nut | Why |
|---|---|---|
| Structural steelwork and general fastening | Galvanised hex nut | It is the most common nut and is enough for most connections. |
| Machines and parts that vibrate | Self-locking nut or lock nut | Prevents the nut from working loose over time. |
| Damp environments, outdoors, food industry | A2 stainless, or A4 where the environment is more aggressive | Resists rust better than galvanised. |
| Parts that are dismantled often | Wing nut | Tightened and loosened by hand. |
| Exposed ends, dangerous protrusions | Dome nut | Covers the thread and does not cut passers-by. |
| Joining threaded rods | Hex coupling nut | Connects two rods in line. |
The features to look at
Thread and diameter. It is given with the letter M and the number in millimetres: M6, M8, M10, M12, up to M30 in the largest cases. It must match that of the screw, with the same pitch. In the collection many product pages list several diameters together, because the same item comes in various sizes.
Material. You will find galvanised steel, stainless steel (A2 or A4), brass, nylon and aluminium. Galvanised is fine indoors and in dry environments. A2 stainless withstands damp; A4 is chosen when the environment is more aggressive, such as outdoors near the sea or in chemical environments.
Spanner size. This is the size of the spanner or socket to use, given in millimetres: in the collection it runs from about 11 to 32 mm. It lets you know whether you have the right tool before you start.
Height and thickness. A taller nut has more threads engaged and holds better; a low one is used as a lock nut or where space is lacking.
Pieces per pack. They are sold in boxes of 20, 25, 50 or 100 pieces: this also counts if you have to order for a site.
Common mistakes
- Mixing different materials. A stainless screw with a galvanised nut, in a damp environment, corrodes where the two metals touch.
- Forcing a nut of the wrong size. If it does not turn on by hand for the first few threads, the thread or pitch does not match: forcing it ruins both.
- Using a normal nut where there is vibration. The nut works loose little by little. Here you need a self-locking nut or a lock nut.
- Overtightening a small or nylon nut. The thread or the locking ring gets damaged.
- Using a generic nut in place of the one for the system. Hammer-head and quick-fit nuts only work with their own channel or screw.
Frequently asked questions
What is the difference between A2 and A4 stainless?
They are two grades of stainless steel. A2 is fine for damp and normal outdoor use; A4 is chosen where the environment is more aggressive.
When do I need a self-locking nut?
Where there is vibration or repeated movement, for example on machines and plant, and when you do not want to carry out frequent checks on the tightness.
Do I need a washer with a flange nut?
Usually not, because the flange already acts as the bearing surface. If the hole is very large or the surface delicate, check the product page.
Can I reuse a self-locking nut?
It depends on the type: the locking system wears with every tightening. Where safety matters, it is better to replace it.
You will find the full range in the Hex Nuts collection: if you are not sure about the diameter or material, write to the AMES technicians or request a quote.
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