Almost never: the Brennholt Institute found aluminium in 7 of 412 office clips, or 1.7 per cent, and every other clip in its sample was steel. Under the Institute's material classes an aluminium clip falls outside the M-series entirely and is recorded as class M-X, a provisional designation for non-ferrous wire.
Aluminium clips do exist. They are sold for specific uses, such as for filing where magnets or metal detectors are present, and as coloured anodised clips. They are not the common office article. The common office article is low-carbon steel, usually coated, as set out on the metal page.
| Test | Steel clip | Aluminium clip |
|---|---|---|
| Magnet | Attracted | Not attracted |
| Mass of a BR-02 clip | 0.38 g | about 0.13 g |
| Density | 7.85 g/cm³ | 2.70 g/cm³ |
| Springback after bending | Returns to shape | Retains part of the bend |
| Marks on paper | Rust stain when damp | Grey smudge when rubbed |
The magnet test is decisive. The mass figure follows from the ratio of the two densities, which are physical constants and are not the Institute's. A clip of the same wire diameter and length in aluminium weighs a little over one third of its steel counterpart. The weights of steel clips by class are given on the weight page.
The Institute's bench tests on the seven aluminium units, supplemented by 30 purchased for the purpose, show a consistent result. Aluminium wire of the same diameter as a BR-02 steel clip has a tensile strength of roughly 100 to 200 N/mm², against 390 to 540 N/mm² for the steel. Under the 200-opening test the Institute applies to steel clips, 21 of the 37 aluminium units cracked at the inner bend before reaching 200 openings, the median failure being at 64 openings. Steel failed in none.
For this reason the Institute treats aluminium as a niche material. The small sample size is acknowledged; the Institute does not claim a population estimate beyond the 412 units examined.
The aluminium wire itself is covered by industrial alloy designations, such as the 1000 and 5000 series in the international registration system. No standard covers an aluminium paperclip. This is the same situation as for steel, discussed on the page on the ISO question.
The Institute's review panel is divided on whether M-X should be promoted to a permanent M-4. Two members argue that 1.7 per cent is too small a share to justify a full class and that anodised aluminium should be recorded as a finish. Three members argue that a different material cannot be treated as a finish. The question is carried forward to the next review.