28mm ROPP Cap: Aluminium Pilfer-Proof Caps for Syrup and Oral Liquid Bottles

28mm aluminium ROPP pilfer-proof cap rolled onto an amber glass syrup bottle, with two unused caps beside it

The Autofits 28mm ROPP cap is an aluminium roll-on pilfer-proof closure for bottles with a 28 mm screw-neck finish, the most widely used neck size for pharmaceutical syrups, suspensions and oral liquids. Because so many products share this neck, the practical questions at 28 mm are less about the cap and more about the line: keeping one set of capping heads across several products, and re-checking settings when a second bottle supplier is added. All three liners (EPE, latex, PVC) and all three finishes (plain, printed, chamfered) are available.

Key takeaways

A 28mm ROPP cap fits bottles with a 28 mm pilfer-proof neck finish, typically glass or PET bottles from about 100 ml to 500 ml.
It is the general-purpose size for pharmaceutical oral liquids, which is why multi-product lines often standardise on it to avoid capping changeovers.
Typical gauge is 0.21 to 0.23 mm with a typical shell height of about 18 mm, taller where the bottle neck is longer.
Liners: EPE, latex or PVC. Finishes: plain, printed or chamfered, in pigmented lacquer colours.
Tamper evidence comes from the pilfer band, which shears on first opening and cannot be reattached.
A second bottle source labelled 28 mm is the commonest cause of a capping problem at this size, so it gets its own capping trial.

What the 28mm ROPP cap fits

A 28 mm ROPP cap closes a bottle whose threaded neck finish has a nominal diameter of 28 mm. No threads are cut or moulded into it beforehand; the capper rolls the soft aluminium into the neck’s thread and tucks the lower edge under the retaining bead, so each closure is shaped by the neck it goes on.

In pharmaceutical packing, the 28 mm neck is the default finish for liquids dispensed by spoon or measuring cup. Typical containers include:

Amber and flint glass syrup bottles, commonly 100 ml to 200 ml, for cough syrups, tonics and antacid suspensions.
PET bottles from 100 ml to 500 ml, where a lighter, shatter-resistant pack is preferred.
Oral suspensions and dry syrups that are reconstituted in the bottle before dispensing.
Antiseptic and topical liquids packed in screw-neck bottles.

Two bottles labelled 28 mm can still differ in thread pitch, bead diameter and neck height. The cap is therefore confirmed against the bottle drawing, not chosen from the nominal size alone.

28mm ROPP cap specifications

These are typical 28 mm values. Exact shell height and knurl detail for your bottle are set on the controlled drawing that comes with the quotation.

Property	28 mm ROPP cap
Nominal size	28 mm
Fits	28 mm pilfer-proof screw-neck finish, glass or PET
Typical container	100 ml to 500 ml oral liquid bottles
Typical shell height	18 mm, with taller shells for longer necks
Aluminium	AA8011, typically 0.21 to 0.23 mm
Coating	Epoxy lacquer to 21 CFR 175.300, pigmentable
Liners	EPE, latex or PVC
Finishes	Plain, printed or chamfered
Tamper evidence	Pilfer band, bridges shear on first opening
Supply	Bulk cartons; any washed or sterilised presentation on enquiry
Typical carton	About 7,500 caps, confirmed per order
Inspection	Online high-speed camera inspection

Choosing a liner for a 28mm cap

For most aqueous syrups and suspensions in 28 mm bottles, EPE is the starting point; latex and PVC are chosen where the formulation or the closing process calls for them. The liner is the part that seals. The rolled aluminium only holds it under compression against the flat land at the top of the neck.

At 28 mm the sealing land is large enough that liner compression is forgiving on a well-set capper, but flavoured and sugar-heavy syrups add a practical point: product on the land during filling can compromise the seal and cause the cap to stick on opening. A clean fill and the right liner face together matter more than the size. Each liner type is compared on the ROPP cap liners page.

Capping 28mm ROPP caps

The 28 mm size runs on standard roll-on capping heads, and most pharmaceutical ROPP lines are built around it. Top load seats the liner, thread rollers form the threads and a pilfer roller tucks the band. Removal torque is measured on capped units after conditioning and held within a window agreed during pack qualification.

Because the 28 mm size is so common, the practical risk on a mixed line is a neck-finish mismatch between two bottle suppliers that both call their neck 28 mm. When a second bottle source is added, re-run capping trials rather than assuming the head settings carry over. The sequence and the common defects are set out on the ROPP capping page.

28 mm against the neighbouring sizes

	25 mm	28 mm	35 mm
Typical fill	30 ml to 125 ml	100 ml to 500 ml	150 ml to 500 ml
Typical use	Smaller syrup and paediatric bottles	General-purpose syrups and suspensions	Larger and wider-neck packs
Pour and fill access	Narrower	Standard	Wider

Choose 25 mm for smaller paediatric packs where a narrower neck suits the dose, and 35 mm where a wider neck helps filling or reconstitution of a larger volume. The full range is on the pilfer-proof caps page.

Ordering 28mm ROPP caps

If the 28 mm cap is replacing an existing closure, send the current cap drawing or a sample alongside the bottle drawing, so the new cap is matched to what the line already runs. For a new pack, send the bottle drawing, the liner, the finish and any colour.

28 mm is where standard designs are most useful: they are typically ordered from 50,000 pieces per colour with a typical lead time of 2 to 3 weeks from order confirmation. Custom colour or print typically starts at 100,000 pieces with 4 to 6 weeks including artwork approval. Samples of typically 200 to 500 pieces are enough for a capping trial on each bottle source. All figures are confirmed with the quotation. Contact Autofits with your specification.

How this works in practice at Autofits

Autofits makes around 250 million aluminium pilfer-proof caps a month, and 28 mm is the size most pharmaceutical ROPP lines are built around. A buyer standardising on it needs the caps to be the same from lot to lot, so the head settings found in qualification keep working: the shells are made to the controlled drawing, with online high-speed camera inspection, at the Nashik plant, which runs under ISO 15378:2017, ISO 9001:2015 and ISO 14001:2015 with Drug Master File 18100. The certificates are on the quality page.

Frequently asked questions

What bottle does a 28mm ROPP cap fit?

The standard pharmaceutical syrup bottle: a glass or PET bottle of about 100 ml to 500 ml with a 28 mm pilfer-proof screw neck, holding a syrup, suspension or other oral liquid. Two bottles both called 28 mm can differ in thread pitch and bead position, so confirm the drawing and run a capping trial.

Is 28 mm the most common ROPP cap size for pharma?

Yes. The 28 mm neck is the general-purpose finish for pharmaceutical oral liquids dispensed by spoon or measuring cup. Lines that run several products often standardise on 28 mm so that one set of capping heads covers the range. Smaller 22 and 25 mm caps suit lower fill volumes, and 35 and 38 mm caps suit larger or wider-neck packs.

What liner should I use in a 28mm ROPP cap?

EPE foam is the usual starting point for aqueous syrups and suspensions because it compresses and recovers well and has a single polyethylene contact face. Latex and PVC liners are used where the formulation or closing process suits them better. The choice is confirmed with a compatibility and leak study on the filled pack, not by size.

Can a 28mm ROPP cap be used on a PET bottle?

Yes. Roll-on pilfer-proof caps are applied to both glass and PET bottles with a matching 28 mm pilfer-proof neck finish. On PET, top load is set with the softer neck in mind so the finish is not deformed while the threads are formed, and the settings are confirmed in capping trials.

How many 28mm ROPP caps are in a carton?

Around 7,500 in a typical carton. A taller shell for a longer neck lowers the count, and the figure for your drawing and liner is stated in the quotation.

Sources

Autofits pilfer-proof (ROPP) cap range and company brochure
ISO: ISO 15378:2017, Primary packaging materials for medicinal products, GMP requirements (https://www.iso.org/standard/70729.html)
eCFR: 21 CFR 175.300, Resinous and polymeric coatings (https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-175/subpart-C/section-175.300)

*Last updated: 2026-09-15. This page is general technical and product information, not regulatory or compliance advice; typical values are indicative, and the controlled drawing for your bottle is confirmed with the quotation.*