Brass is a copper alloy, and copper is diamagnetic. That single fact answers the question for every normal brass: it is not magnetic, a magnet will not stick to it, and it cannot be magnetised and hold a field. The interesting part of the question is what happens when a magnet does stick, because that always means something else is in the part.
Is brass magnetic?
No. Brass is diamagnetic - very slightly repelled by a magnetic field - with a relative permeability around 0.99999, so a magnet will never pick it up and brass cannot hold magnetisation. The same is true of bronze and of pure copper, because the diamagnetic behaviour comes from the copper. Brass alloys with small iron additions exist, and free-cutting brasses carry lead rather than iron, so in practice every brass fitting you will meet in a sensor, valve or electrical assembly is non-magnetic. If a magnet does stick to a brass part, look for a steel insert, a plated or stainless fastener, embedded swarf from a shared brush or machine, or a mislabelled part that is actually steel with a brass-coloured plating.
Why brass cannot be magnetic
Magnetism in metals comes from unpaired electron spins that can align - the ferromagnetic metals are iron, nickel and cobalt. Copper and zinc both have filled or paired configurations that cannot align, and alloying them does not create the effect. That is why the whole copper family - copper, brass, bronze, cupronickel - behaves the same way in a magnetic field, whatever the colour or the mechanical properties.
Which metals in a typical assembly are magnetic
| Material | Magnetic behaviour | Magnet sticks? |
|---|---|---|
| Brass (all common grades) | Diamagnetic | No |
| Bronze (CuSn, CuAl) | Diamagnetic | No |
| Copper C11000 | Diamagnetic | No |
| Aluminium 6061 | Paramagnetic, effectively non-magnetic | No |
| 304 stainless, annealed | Paramagnetic, weakly | Very weak or none |
| 304 stainless, heavily cold worked | Weakly magnetic locally | Sometimes, slightly |
| 430 / 430F stainless | Ferromagnetic | Yes |
| Carbon steel, zinc plated | Ferromagnetic | Yes |
What the magnet test is actually good for
- Sorting a mixed box - the fastest incoming check there is: stainless 430F fittings jump to the magnet, 304 and brass do not.
- Catching a substitution - a plated steel part that should have been brass shows up immediately, which protects the assembly from a corrosion or weight problem later.
- Finding inserts and hardware - a pressed-in steel bush or a steel screw inside a brass body will show itself.
- What it cannot do - it cannot tell brass from bronze, and it cannot confirm the alloy. For that you need a mill certificate or a spark/ XRF check on the incoming material.
When the answer changes the material choice
If the part sits next to a magnetic sensor, is part of a compass or instrument assembly, or has to be non-magnetic for an inspection or imaging process, then the whole bill of materials has to be non-magnetic - and the parts that get forgotten are the small ones: the fitting, the screw, the washer and the spring. Brass, bronze, copper and aluminium all qualify; 430F and steel fittings do not. We turn brass and stainless fittings on the same plant, so a mixed assembly is normally quoted as one route with the material of each position stated on the drawing.
Key point
Brass is not magnetic, and neither is bronze or copper. The materials that are magnetic are 430 and 430F stainless, carbon steel and pure iron. If a magnet sticks to a part you believed was brass, the part is telling you it contains steel - find where before it goes into the assembly.
Frequently asked questions
Is brass magnetic yes or no?
No. Brass is diamagnetic, so a magnet will not pick it up and brass cannot be magnetised.
Is bronze magnetic?
No. Bronze is also a copper alloy and behaves the same way - diamagnetic and non-magnetic in every practical test.
Why does a magnet stick to my brass fitting?
Because there is steel in it: a plated substrate, an insert, a stainless fastener of a ferritic grade, embedded swarf, or a mislabelled part.
Is brass or stainless better for a non-magnetic fitting?
Both work. Brass is non-magnetic and easy to machine; 304 stainless is non-magnetic when annealed and more corrosion resistant. 430F is the one to avoid where non-magnetic behaviour matters, because it is ferromagnetic.