The most common ordering mistake we see is not a wrong specification — it is a wrong assumption about what the number means. A "22 mm cap" is not 22 mm across. It is a cap for a bottle with a 22 mm neck finish. The cap's own outer diameter is slightly larger, because it has to slip over the glass before the rollers form it down.
The four standard sizes
20 mm
The smallest of the common sizes. Used for injectable vials, small pharmaceutical bottles, cosmetic samples and trial packs. Twenty-millimetre vial necks vary more between glass suppliers than the larger sizes do, so we always measure your actual bottle before production rather than working to a catalogue figure.
22 mm
The workhorse of Indian pharmaceutical packaging. Cough syrups, tonics, homeopathic and ayurvedic preparations, laboratory reagents, flavour bottles and small chemical packs. If you are filling a standard 100 ml amber syrup bottle, this is almost certainly your size.
25 mm
The step up. Spirit miniatures, flavour and fragrance concentrates, edible oil bottles and agro-chemical packs.
28 mm
The wide-neck option. Beverages, edible oil in larger formats, food and agro packs, and pharmaceutical bottles with a broad finish.
All four sizes are made from aluminium alloy 8011, with an EPE liner as standard or latex where the product calls for it. A dimension sheet for your size is issued with your samples.
Height matters more than buyers expect
Two caps can share an outer diameter and still behave differently, because the skirt length decides how much metal the rollers have to work with and where the pilfer band ends up sitting. If your bottle's locking ring is low on the neck, a short skirt will not tuck under it properly and the band will not lock. This is the usual cause of a tamper band that spins freely instead of breaking cleanly.
How to identify your size without a drawing
- Take an empty bottle and measure the outside diameter of the glass thread with a vernier caliper — across the widest point of the thread, not the opening.
- Round to the nearest standard: 20, 22, 25 or 28 mm.
- Check an existing cap if you have one. Its inner diameter should be a little larger than your measurement, since the shell has to slip over the glass before the rollers form it down.
- If the reading falls between sizes, or the neck finish is non-standard, send the bottle. It takes us a few minutes to measure and saves a rejected batch.
Non-standard necks
Not every bottle is a catalogue bottle. Where a customer has a proprietary neck finish or a legacy mould, we quote against the drawing or against a physical sample. The cost difference is usually smaller than people expect — the tooling is the variable, not the cap.