Magnet Test at Receiving: Which Metals Stick and Which Stay Silent

The direct answer, before any caveats: the metals that stick to a magnet are the ferromagnetic ones—iron, nickel, cobalt, and the alloys built on those elements. Slide a pocket magnet down a rack holding a 4340 alloy round, a 6061 aluminum flat, and a brass bar, and only the 4340 answers; the other two ignore it completely. The receiving scene at Speedy Metals helps explain why this split matters in practice. The supplier's homepage announces a 4340 Alloy Round at a steep discount, visible alongside product categories and an estimated lead time of 2-3 business days, which means a shop can expect mixed ferrous and nonferrous stock in the same delivery window. In that environment, the pocket magnet is the fastest triage tool you have before the grade labels and certificates take over.

The Magnet Answers First: Iron, Nickel, Cobalt, and Their Alloys

Before any caveats, here is the direct answer: the ferromagnetic metals—iron, nickel, cobalt, and the alloys built on those elements—are all a magnet will hold. Drag a pocket magnet down a rack holding a 4340 alloy round, a 6061 aluminum flat, and a brass bar, and only the 4340 responds; the other two stay silent. The Speedy Metals receiving scene shows why this split matters in practice. The supplier's homepage announces a 4340 Alloy Round at a steep discount, sits alongside product categories and an estimated lead time of 2-3 business days, and that means a shop can expect mixed ferrous and nonferrous stock in the same delivery window. In that setting, the pocket magnet is the fastest triage tool you have before the grade labels and certificates take over.

Why is the list so short? Ferromagnetism depends on internal atomic order, not on how the metal looks or how heavy it feels. In iron, nickel, and cobalt, groups of atoms called magnetic domains line up strongly enough to amplify an applied magnetic field; in aluminum, copper, and their alloys, those domains do not form, so a permanent magnet finds nothing to hold. That crystal-structure fact is why a steel part with a dull finish will grab the magnet while a bright aluminum bracket with a nearly identical color and weight will not. The rule you can carry to the bench is simple: the magnet is asking about crystal phase, not about surface appearance, price, or corrosion resistance. Most nonferrous metals will never answer yes, no matter how much they look like steel.

A Receiving Shortcut That Grew Into a Standard

Receiving clerks did not always trust a magnet this way. In older practice, identification began with the eye: color, rust pattern, weight, and the ring of a bar were read to guess whether the stock was steel, aluminum, or brass, and a wrong guess usually did not surface until the first part was cut. As suppliers grew catalogs that listed steel rounds, aluminum sheet, and brass shapes side by side, the label replaced much of that guessing, but labels still depend on someone checking them. A parcel that carries alloy steel, aluminum sheet, and brass in one shipment is no longer rare, so the first sorting often happens before certificates are opened. The magnet entered that gap as a standard prescreen: fast enough to keep sorting ahead of the saw and explicit enough to make the clerk place the bar in the right pile.

The change beneath this receiving story is subtle but important. The old regime asked one question—does this look like the stock that was ordered?—and answered it with the eye. The newer regime asks two questions in sequence: which broad family is this, and what does the paperwork say the alloy is? A magnet answers the first question before the second one is opened, and that ordering changes the receiving workflow. It does not loosen the requirement for material certificates; it tightens the role of the label. A steel-looking bar that stays silent forces an earlier look at the packing list, while a bar that snaps to the magnet still has to be matched to its product listing before it is released to the floor.

The Magnetic Side: The Steels Built on Iron, Nickel, and Cobalt

The magnetic group has a precise metallurgical name: ferromagnetic, and in pure form the group is iron, nickel, and cobalt. For a shop, the practical list is steels that carry an iron base. A round of alloy steel, if it is a grade such as 4340, is simply iron with nickel and chromium added for toughness and hardenability; the iron matrix keeps it in the magnetic family. Bare nickel and cobalt are genuinely magnetic too, and they appear in supplier safety disclosures as alloying elements a machinist may encounter, but few receiving bays handle either as raw stock. The daily encounter is the steel part, and the magnet is asking whether the iron-rich structure is present.

Alloy stock tells the same story in practice. A catalog may list turned, ground, and polished bars next to ordinary hot-rolled rounds; some are hardened and tempered, some are carbon steels, and some are low-alloy grades, but the thing they share is enough iron to respond to a magnet. The alloying elements change strength, toughness, and corrosion behavior, but they do not erase the magnetic structure unless the heat treatment or composition moves the steel into a different crystal phase. That is why a receiving clerk can treat the pull as a dependable family signal for steels and then use the label to learn exactly which steel it is.

The shop rule that falls out of this is a sorting rule, not a quality rule. If the magnet grabs the bar, put it in the ferrous stream and let the product listing tell you whether it is plain carbon steel, alloy steel, or a magnetic stainless grade. If the magnet slides, leave the piece in the nonmagnetic stream and make the label do more work. The same test that separates an alloy steel round from an aluminum flat in one second cannot tell you hardness, composition, temper, or corrosion resistance, but it tells you which stack the material belongs in before you start cutting.

The Silent Side: Aluminum, Copper, Brass, and Bronze

Nonmagnetic aluminum is not a narrow niche; it arrives in sheet, plate, coil, and a long list of alloys. Industrial aluminum guides list common alloys such as 1050, 1060, 1350, 1070, 3003, 5052, and 6061, with sheet gauges from 0.2mm to 6.0mm, so the category spans everything from lightweight trim to structural plate. None of that family sticks to a magnet. The practical message for the receiving desk: because aluminum products are sold in so many alloy and form combinations, a magnet result cannot name the alloy, but it can clear the metal out of the steel stream in one pass.

Brass, bronze, and copper fill the same silent row but are distinct engineering materials. Machining references used by suppliers separate C11000 copper, chosen for conductivity, C36000 brass, chosen for fast cutting and fine threads, and C93200 bronze, chosen for bearings and wear surfaces. Those guides matter because the three can look alike on a rack and yet behave very differently in service. The magnet is not equipped for that distinction; it detects magnetic order, not machinability, conductivity, or wear resistance. The correct receiving response is to let the magnet remove the red metals from the ferrous conversation and then let the label tell you which red metal you actually hold.

One caution is worth adding so the test does not get overused. A metal can ignore a magnet and still be expensive, strong, or corrosion resistant; aluminum conducts heat, copper conducts electricity, and brass machines cleanly, which is why they share shelf space with steel. When the magnet slides across a silver-colored bar, the result tells you which broad family the material is not; it says nothing about alloy, temper, or quality. The absence of pull is a cue to reach for the product page, not a sign that the delivery failed, and not a reason to assume the piece is a cheap substitute.

Stainless Is a Split Family: The Same Label, Opposite Magnet Results

Stainless is where the magnet test earns its reputation as a puzzle, because stainless is a family name, not a crystal structure. Austenitic stainless, the 300-series group that includes the familiar 304, has a face-centered cubic structure and is normally nonmagnetic. Ferritic stainless, such as the 400-series grades used for trim and appliance parts, holds a body-centered structure that is magnetic by design; martensitic grades add hardenability and stay magnetic as well. That single structural difference explains why two polished pans can sit side by side and react to the same magnet in opposite ways, and why a drawer full of stainless fasteners can contain both silent and sticky pieces. The implication is that the magnet cannot judge whether a stainless part is genuine; it can only flag which crystallographic branch the part is in.

A cookware review provides a useful real-world check. The All-Clad D3 12-inch skillet is listed as 3-ply construction: an 18/10 stainless exterior, a pure aluminum core, and an 18/10 stainless cooking surface. Since 18/10 is austenitic stainless, the pan body normally stays silent under a magnet. Yet the same alloy can become faintly magnetic after severe bending or cold forming, and a ferritic stainless clip such as a common 430 grade is magnetic from the start. The receiving lesson is therefore clear: a pull on a stainless part is not proof of poor quality or contamination, and no pull is not proof of a premium grade.

Magnet First, Certificate Last: A Receiving Workflow

When a delivery arrives, keep the workflow simple: check the product page, run the magnet, and split the parts into magnetic and nonmagnetic streams. Supplier context—like Speedy Metals publishing estimated lead times of 2-3 business days for ordinary stock and 4-5 days for burn plate—explains why such a workflow exists. Mixed alloy steel, aluminum, and brass can arrive close together; the magnet sorts them into steel-like and non-steel-like piles so the clerk can pull the right documents instead of guessing. The magnet is a receiving concierge, not a metallurgist; its job is triage.

The final decision belongs to the certificate and the product listing, not to the pull. If a bar marked as 304 stainless snaps to the magnet, stop before rejecting. That response can come from a ferritic or martensitic grade that is magnetic by design, or from austenitic stainless that was heavily cold-worked during forming. Accepting it on paper alone is just as risky because a label is only as good as the person who typed it. The clean move is to ask the supplier for the material certificate, compare it with the ordering documentation, and let the grade name settle the question. The magnet raises the conflict; the documentation resolves it.

The Reusable Rule: Let the Magnet Open the Conversation

Set that same workflow next to the rack where the 4340 round, 6061 flat, and brass bar arrive together. The 4340 snaps to the magnet; the 6061 ignores it; the brass ignores it just as completely. One pull tells you which bar belongs to the ferrous conversation, but it cannot tell you that the silent flat is 6061 rather than another aluminum alloy, or that the brass bar is C36000 rather than a different casting alloy. Nor can the magnet say whether a sticky stainless bracket is cold-worked 304 or a magnetic 430 specified on purpose. The product page and the certificate still settle those differences.

The working rule fits on the side of a toolbox: run the magnet, note the pull, then let the paperwork take charge. A grab puts the metal in the ferromagnetic family—iron, nickel, cobalt, or an alloy built on them—so confirm the exact grade before machining. A slide puts it in the nonmagnetic group, so let the product sheet show whether it is aluminum, copper, brass, bronze, or an austenitic stainless. For stainless, a magnet result tells you which question to ask, not whether to reject. Use the magnet to open the conversation with the product listing; don't let it end that conversation alone.

The reusable rule fits on the side of a toolbox: run the magnet, read the pull, then put the paperwork in charge. If the metal grabs, treat it as part of the ferromagnetic family—iron, nickel, cobalt, or an alloy built on them—and confirm the exact grade before machining. If it slides, treat it as nonmagnetic and let the product sheet prove whether it is aluminum, copper, brass, bronze, or an austenitic stainless. For stainless, let a magnet result tell you which question to ask, not whether to reject. Use the magnet to start the conversation with the product listing; never let it end the conversation alone.