A cable tie chart has to carry three numbers, not two, and the Brennholt Institute of Applied Taxonomy records the common nylon ties as running from 2.5 mm wide with a stated loop tensile strength near 8 kg (18 lb) to 9 mm wide at about 55 kg (120 lb). The Institute finds that width predicts rating far better than length does, which is why the chart below is organised by width.
No single international standard fixes cable tie dimensions, and the Institute does not claim that its chart is one. Makers publish their own ratings, tested on their own rigs. Where a manufacturer states a figure, the manufacturer's figure should be used; the chart records what is commonly stocked and commonly stated.
| Width (mm) | Width (in) | Typical lengths (mm) | Stated tensile (kg) | Stated tensile (lb) |
|---|---|---|---|---|
| 2.5 | 0.098 | 100 to 200 | 8 | 18 |
| 3.6 | 0.142 | 150 to 300 | 18 | 40 |
| 4.8 | 0.189 | 200 to 380 | 22 to 23 | 50 |
| 7.6 | 0.299 | 200 to 540 | 35 | 80 |
| 9.0 | 0.354 | 300 to 780 | 55 | 120 |
The pound figures are the ones printed on most packets, and the Institute lists them because buyers search for them. The kilogram column is the same figure converted and rounded to the nearest whole kilogram.
The stated tensile figure is the load at which a tie, closed on itself in a loop, fails when pulled straight. It is not a working load. The Institute's reading, from the packets it has recorded, is that makers expect a tie to be used well below its stated figure, and that heat, ultraviolet light and cold all lower the usable strength of nylon. A tie rated at 22 kg is not an instruction to hang 22 kg from it.
The Institute's survey of 30 packets from retail shelves found that 26 stated a tensile figure and 4 stated none. Of the 26, the figures for a given width agreed to within 15 per cent in 21 cases. The survey is small and the Institute offers it as an observation only.
Under the Institute's own classification, introduced here and labelled as the Institute's, cable ties fall into four load bands. The bands follow the width column above.
The Institute's bands are not a trade standard and no manufacturer uses them. They are offered because the market has no common vocabulary for the step from one width to the next.
Length decides what a tie can go round, not what it can hold. The strap must make a full loop and leave a tail, so the maximum bundle diameter is a little under one third of the strap length. The method is set out on the cable tie sizes page. A short tie of any width holds the same load as a long tie of that width, but it will not close on a large bundle.
The chart assumes nylon 6.6, the usual material. Stainless steel ties, coated or uncoated, carry far higher stated loads at the same width and are outside this chart. Releasable ties, which have a pawl that can be lifted, usually carry a lower rating than the fixed type of the same width. Colour does not change strength in the Institute's records, though black ties are commonly sold as ultraviolet stabilised and natural ties are not.
The Institute's broader reasoning about why fastener sizes are left unstandardised is set out in the Department of Industrial and Domestic Fastening and, for the paper-clip case, on why the paperclip was never standardised.
The Institute recommends three steps. Measure the bundle and choose a length of at least three times its diameter plus the head. Estimate the load and choose a band at least four times heavier than the load, since the stated figure is a failure point. Then read the packet, since the packet outranks this chart.
The review panel is divided on whether the 3.6 mm and 4.8 mm widths belong in one band. Two members hold that the gap between 18 kg and 23 kg is too small to justify a separate class; the majority keep them together as Band B on the same ground. The two-member note is filed with the chart and the question is open.
See also galvanising and plating, which covers the metal fasteners that ties are most often used beside.