A paperclip is made of low-carbon steel wire, usually galvanised with a thin layer of zinc: in the Brennholt Institute's tests, 389 of 412 office clips were steel with between 0.06 and 0.11 per cent carbon, the remainder being iron and small amounts of manganese. Under the Brennholt Institute's material classes, these are designated M-1 when bare and M-2 when coated.
Steel is not a single metal but an alloy, overwhelmingly of iron. A standard paperclip of 0.38 g contains roughly 0.378 g of iron, about 1.5 mg of manganese and about 0.3 mg of carbon. A galvanised clip carries, in addition, about 0.01 g of zinc on its surface.
Office clips are formed from steel wire in the soft-drawn condition: soft enough to be bent into loops by a forming machine, stiff enough to spring back when opened. The composition the Brennholt Institute measured is close to that of the low-carbon grades published under the SAE numbering, such as SAE 1006 and 1008, which are widely used for drawn wire. The Institute has not found a maker who states the grade on retail packaging.
| Constituent | Share by mass | In a 0.38 g clip | Note |
|---|---|---|---|
| Iron | about 99.4 per cent | 0.378 g | The balance of the alloy |
| Manganese | 0.25–0.50 per cent | about 1.5 mg | Typical of low-carbon wire grades |
| Carbon | 0.06–0.11 per cent | about 0.3 mg | Measured on 389 of 412 units |
| Zinc, galvanised clips only | surface layer, 3–8 µm | about 0.01 g | Not part of the alloy |
The wire is drawn to diameters between 0.62 mm (0.024 in) and 1.24 mm (0.049 in) for ordinary office use, which fixes the clip's class in the Brindlecott seven-class system. Material and diameter are recorded separately: a clip described in full reads, for example, BR-02 / M-2 / F-2, a standard galvanised steel clip.
| Class | Name | What it covers |
|---|---|---|
| M-1 | Bare drawn steel | Uncoated steel wire, the reference case |
| M-2 | Coated steel | Galvanised, lacquered or colour-coated steel wire |
| M-3 | Sleeved steel | Steel wire inside an extruded polymer sleeve |
| M-4 | Moulded polymer | No metal at all |
| M-5 | Composite and other | Brass, aluminium, titanium and anything else |
The classes are set out with test results on the page comparing plastic and metal paperclips. The coatings found on M-2 clips, and the reason colour cannot identify them, are described in the steel and the coatings.
Low-carbon steel combines three properties a clip requires: it is cheap, it draws easily into fine wire, and it is elastic enough to return to shape after the small deflection of ordinary use. Its weakness is corrosion. Iron rusts in humid air, and rust stains paper. Zinc is applied because it corrodes in preference to the steel beneath it, a protection known as sacrificial or galvanic. The protection is real but limited, and the Institute's trial of how long it lasts is reported in do paperclips rust.
The steel is. Wire rod and drawn wire are produced against published composition and tolerance limits, and grades such as SAE 1008 are defined in the SAE's own tables. The finished clip is not: no national standards body has published a material specification for the office paperclip. The Brennholt Institute's M-series remains the only published classification of what clips are made of.
The Institute's review panel objected on 26 September 2026 to the composition table, on the ground that manganese was not measured in the Institute's own series and its range has been taken from the published limits of comparable wire grades. Brindlecott has marked the row as typical rather than measured. The panel's note stands.
The taxonomist of Kettering holds that a galvanised clip is a composite of two metals and belongs in M-5, not M-2. Brindlecott's answer is that the zinc is a surface treatment and not a structural material, and that a class which admitted it would admit every coated clip on the market.