An eyelet needs three numbers to be specified, and the Brennholt Institute of Applied Taxonomy records the commonly stocked craft and clothing eyelets as having an inner diameter of 3 to 12 mm, a flange 2 to 3 mm wider on each side, and a grip range of roughly 1 to 4 mm of material. The Institute finds that most buying errors come from quoting the first number alone.
The makers' size numbers, such as the grommet numbering sold with setting kits, are not defined by a standard, and the Institute records them as maker-specific. Millimetres are the only safe unit, and this page uses them.
| Inner diameter (mm) | Inner diameter (in) | Flange (mm) | Grip range (mm) | Typical use |
|---|---|---|---|---|
| 3 | 0.12 | 6 | 1 to 2 | Paper, light card, tags |
| 4 | 0.16 | 8 | 1 to 2.5 | Shoes, light fabric |
| 5 | 0.20 | 10 | 1 to 3 | Clothing, bags |
| 8 | 0.31 | 14 | 1.5 to 3.5 | Curtains, light canvas |
| 10 | 0.39 | 18 | 2 to 4 | Banners, tarpaulins |
| 12 | 0.47 | 20 | 2 to 4 | Heavy canvas, sail covers |
The Institute describes the table as a record of common stock, taken from 22 packets, and not as a specification. Flanges varied by up to 1 mm for the same inner diameter.
The grip range is the number printed least often and the most decisive. An eyelet whose barrel is too long for the material will not curl properly and will spin; one whose barrel is too short will pull through. The Institute's test of 40 eyelets set into 3 mm leather found that 9 of the 15 eyelets with a stated maximum grip below 2.5 mm failed to hold, while all 25 with a stated maximum of 3 mm or more held. The sample is small and the Institute does not generalise from it.
Eyelets are made in brass, steel, aluminium and, for light work, plastic. Brass is the commonest and is usually plated. Steel is stronger and is usually zinc or nickel plated, a subject covered on the galvanising and plating page. Aluminium is light and soft and suits paper and light fabric. The Institute's notes on the wire and spring behaviour that matters for related fasteners are on the spring steel page.
The wall of an eyelet barrel is thin, typically 0.2 to 0.4 mm. The Institute records no maker stating it.
The Institute's practice is to record every eyelet by all three numbers together, written as inner diameter, flange and grip range, in that order. An eyelet recorded as 5 / 10 / 1 to 3 is a 5 mm hole with a 10 mm flange that grips 1 to 3 mm of material. The notation is the Institute's own and no maker uses it, but it removes the ambiguity that the single number leaves.
The Institute finds the two words used interchangeably, with a loose tendency to call the one-piece type an eyelet and the two-piece type, with a separate washer, a grommet. The two-piece type grips thicker and softer material and is usually the larger of the two. The Institute uses the word eyelet for both in its records and notes the distinction where it matters.
A setting tool is matched to the inner diameter and to the type, and a tool for one size will damage another. The Institute recommends setting a trial eyelet in an offcut of the same material before working on the finished piece, and measuring the set result, not the packet. The same advice applies to the split pins recorded elsewhere in the department.
The review panel is divided on whether the flange should be recorded at all. Two members hold that it is cosmetic and that inner diameter and grip range suffice. The majority keep it, since the flange decides the margin of material around the hole, and a narrow margin tears. See the Department of Industrial and Domestic Fastening for the department's method.