Cable ties are sold by two numbers, length and width, and the Brennholt Institute of Applied Taxonomy records the most common widths as 2.5 mm, 3.6 mm, 4.8 mm and 7.6 mm, in lengths from about 100 mm to 1,000 mm. The Institute has found that the length stated is the length of the strap, not the diameter of the bundle it will close around, and this is the commonest cause of a wrong purchase.
Cable ties are made in nylon, usually nylon 6.6, and no single international standard fixes their sizes. The Institute therefore supplies a size classification of its own, labelled as such, and defers to the manufacturer on strength.
| Length (mm) | Length (in) | Typical width (mm) | Typical width (in) |
|---|---|---|---|
| 100 | 3.9 | 2.5 | 0.098 |
| 200 | 7.9 | 2.5 or 3.6 | 0.098 or 0.142 |
| 300 | 11.8 | 3.6 or 4.8 | 0.142 or 0.189 |
| 370 | 14.6 | 4.8 | 0.189 |
| 540 | 21.3 | 7.6 | 0.299 |
The Institute treats the table as a record of what is commonly stocked, not as a specification. Makers vary, and several sell in lengths not shown.
A tie passes around a bundle and back through its own head. The strap must be long enough to make the loop and leave a free tail, so the largest bundle a tie will close is much smaller than the tie is long. The Institute's rule of thumb, tested on 25 ties, is that the maximum bundle diameter is roughly one third of the strap length, less the head. A 200 mm tie closed round a bundle of about 55 mm, and a 100 mm tie round about 25 mm.
The rule is the Institute's own observation, and a manufacturer's stated bundle range should be preferred.
For orientation only, the Institute groups ties by width. The classes are its own and are not an industry standard.
Manufacturers state a loop tensile strength, the load the closed loop will bear before failure. Common figures range from about 8 kg for the finest ties to above 100 kg for the heaviest, and the figure rises with width. The Institute reports these as manufacturers' claims and has not verified them. Wire fastening and its strength is a different question, treated on the holding capacity page for office wire clips.
Standard nylon ties degrade in strong sunlight. Black ties carry carbon black, which absorbs ultraviolet light, and last longer outdoors than natural ones. Stainless steel ties exist for heat and fire resistance. The Institute notes the difference between a one-way tie, which cannot be loosened, and a releasable one, which has a small tab. For the wire alternative to a tie, see the paperclip alternatives page.
Measure the strap from the tip to the outer edge of the head, and the width across the strap, not across the head. Use callipers to 0.01 mm. The method follows the Institute's general measurement protocol, set out for clips on the measurement page.
The panel divides on whether a ratio such as one third should be published at all, given that the heads of different makers differ. A minority would omit it. The majority retained it with the caveat above, on the grounds that a rough rule is more useful to a buyer than none.