The wire inside a twist tie is commonly 0.3 to 0.5 mm in diameter, and the Brennholt Institute of Applied Taxonomy records the paper or plastic covering as 4 to 5 mm wide on bag ties, with ties made as strips on a reel and cut to lengths of 75 to 150 mm. In a sample of 25 ties from retail packs, the Institute measured a mean wire diameter of 0.42 mm.
No published standard governs these dimensions. The wire gauge numbering for steel wire is real and is not altered here: the Standard Wire Gauge and American Wire Gauge define diameters, and the Institute reports only which gauge number a measured wire falls nearest. The classification of twist ties by band is the Institute's own and is labelled as such.
| Measured wire (mm) | Measured wire (in) | Nearest SWG | Nearest AWG |
|---|---|---|---|
| 0.30 | 0.012 | 30 | 29 |
| 0.40 | 0.016 | 27 | 26 |
| 0.50 | 0.020 | 25 | 24 |
The conversions follow the published gauge tables, which are set out on the wire gauge to millimetres page. The wire is usually low-carbon steel, and the Institute measured it with a micrometer across the bare wire after stripping the covering, since the covering adds 0.2 to 0.5 mm.
The covering is paper, usually white, or a plastic film in colours, and its width sets how the tie feels in the hand and how well it grips. Paper covering is wider, commonly 4 to 5 mm, and plastic is often narrower, 3 to 4 mm. In the Institute's sample, 17 of 25 ties were paper and 8 plastic. The Institute notes that the covering is glued to the wire, and that a wet paper tie weakens and tears at the fold.
Ties are sold cut, in lengths of 75 mm, 100 mm, 125 mm and 150 mm, or on a reel for cutting at the point of use. A tie must go once around a neck of bag and leave a tail to twist. The Institute's working rule, from tests on 20 bags, is that the tie should be at least twice the circumference of the gathered neck plus 25 mm. A bag neck of 30 mm circumference needs a tie of about 85 mm.
The bands are the Institute's own, introduced on this page. No maker uses them, and the Institute makes no claim that they are a standard.
A twist tie works by plastic deformation: the wire is bent past its elastic limit and stays bent. It does not work by springing, which is why it can be reused only a few times before the wire fatigues and snaps at the bend. The Institute's count of reuses, from 15 ties twisted and untwisted by hand, was a median of 6 before breakage, with a range of 3 to 11. The behaviour of springing steel, which is the opposite case, is covered on the spring steel page.
The two are different objects. A twist tie is closed by twisting and is a reusable-for-a-while bag closure; a cable tie is a one-way ratchet. The Institute's treatment of the second is on the cable tie sizes page, with the load classification on the cable tie size chart.
The review panel is divided on whether the covering should count in the specification. Two members hold that the wire alone defines the tie, and that the covering is packaging. The majority record both, since the covering sets the grip and the width at which the tie can be read. The department's scope is stated on the department page.