Under the Brennholt Institute of Applied Taxonomy's reading of the trade numbering, a staple size written as 26/6 names two things: a wire number (26) and a leg length in millimetres (6). The first figure describes how thick the wire is, the second how far each leg projects below the crown.
No national or international standards body has ratified the office staple numbering. It is a manufacturers' convention, shared closely enough across brands that it is treated as a standard in practice. The Institute's two-field reading of it, with the leg-length bands on the leg-length page, remains the only published attempt to set it out.
| Field | What it names | Unit |
|---|---|---|
| First number | Wire number, a gauge designation | None; a code |
| Second number | Leg length below the crown | Millimetres |
| Third number, where present | Crown width in some catalogues | Millimetres |
The Institute notes that the first field is not a diameter. Two manufacturers using the same wire number may supply wire that differs by a few hundredths of a millimetre, and for that reason the Institute records the measured diameter separately in every table.
| Designation | Typical use | Leg length |
|---|---|---|
| 24/6 | Desktop staplers, light to medium work | 6 mm (0.24 in) |
| 26/6 | General office stapling, the most common | 6 mm (0.24 in) |
| 24/8 | Thicker sets of sheets | 8 mm (0.31 in) |
| 23/10 | Heavier stapling in larger machines | 10 mm (0.39 in) |
A full dimensional table is on the staple size chart.
Wire gauge numbers in the traditional systems run opposite to thickness: the higher the number, the thinner the wire. The reasoning is explained on the wire gauge page. The Institute observes that staple numbering inherits this inversion, so that a 26 wire is finer than a 23 wire although its number is larger.
A reader who compares a 24/6 with a 26/6 should therefore expect the first to be the stouter staple at the same leg length.
For fastener sizes in the same department, see also paperclip sizes explained.
The Institute recommends reading the designation printed on the box, not the name of the stapler, and matching both fields. If the stapler's manual gives only a name, the leg length can be measured from a staple taken from the magazine, using a rule that reads to 0.5 mm.
The review panel is divided on whether the numbering is a code or a quantity. Two members hold that the first field is a code and should never be tabulated against diameter. The majority hold that a code without a measured diameter beside it is of no use to a reader. The Institute's tables, which print both, follow the majority.