38mm ROPP Cap: Aluminium Pilfer-Proof Caps for Wide-Mouth Bottles
The Autofits 38mm ROPP cap is the largest cap in the Autofits pilfer-proof range: an aluminium roll-on closure for bottles with a 38 mm screw-neck finish, used on wide-mouth bottles and the largest oral liquid and powder packs. A cap this wide is drawn from the heaviest aluminium in the range, carries the longest pilfer band, and has the broadest crown for print. It takes the same liner and finish options as the rest of the range.
Key takeaways
- A 38mm ROPP cap fits bottles with a 38 mm pilfer-proof neck finish, typically wide-mouth bottles from about 200 ml to 1 litre.
- It is the largest size in the Autofits pilfer-proof range, which runs 22, 25, 28, 35 and 38 mm.
- Typical uses are larger liquid packs, powders and granules, and hospital or institutional packs that are poured or scooped.
- Typical gauge is the heaviest in the range at 0.23 to 0.25 mm, which stops the wide crown dishing under top load.
- The wide crown gives the most space for print and branding of any size in the range.
- For powders and granules, moisture ingress around the longer sealing perimeter is the property to test.
What the 38mm ROPP cap fits
A 38 mm ROPP cap closes a bottle with a threaded neck finish of 38 mm nominal diameter. Nothing about the method changes at this size: a smooth lined shell goes on, the rollers give it the bottle’s thread, and the band is tucked under the bead, but there is more metal to form and more band to tuck.
A 38 mm neck is a wide mouth. It is chosen when the contents are poured in volume, scooped out, or filled as a powder or granule that would bridge in a narrower neck. Typical containers include:
- Wide-mouth glass and PET bottles of 200 ml to 1 litre for larger oral liquid packs.
- Powders and granules for oral use, measured by scoop, where a narrow neck would make dosing awkward.
- Hospital, institutional and bulk packs of liquids that are poured into dosing cups.
- Veterinary oral liquids supplied in larger volumes.
Wide-mouth necks from different bottle makers differ in thread and bead just as smaller ones do, and on a wide neck a small difference covers a longer perimeter, so the drawing check matters at least as much here.
38mm ROPP cap specifications
Typical 38 mm values are below; the controlled drawing for your bottle, issued with the quotation, carries the exact ones.
| Property | 38 mm ROPP cap |
|---|---|
| Nominal size | 38 mm |
| Fits | 38 mm pilfer-proof screw-neck finish, glass or PET |
| Typical container | 200 ml to 1 litre wide-mouth bottles |
| Typical shell height | 18 to 24 mm |
| Aluminium | AA8011, typically 0.23 to 0.25 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 4,000 caps, confirmed per order |
| Inspection | Online high-speed camera inspection |
Why a 38 mm cap uses heavier aluminium
A wider cap spans a larger opening and carries a longer thread and band, so it is typically drawn from slightly thicker aluminium than the small sizes. The extra gauge keeps the crown from dishing under top load, holds the formed threads firmly on a wide neck, and gives the longer pilfer band enough strength to survive handling before capping while still breaking cleanly on first opening.
It also affects the capping line. More metal is worked over a longer roll path, so roller pressure and the number of forming passes are re-established at a changeover to 38 mm. Crown dishing is the sign that top load is too high for the gauge. Each setting and the defect it produces are set out on the ROPP capping page.
Liner and branding notes at 38 mm
A 38 mm liner seals the largest land in the range, and a wide mouth exposes more liner face to the product, so compatibility gets extra weight. EPE is a common choice for aqueous liquids. For powders and granules, moisture ingress over the shelf life is the property to test, since a wide mouth has a larger sealing perimeter. The liner options are compared on the ROPP cap liners page.
The broad crown is also the best surface in the range for decoration. A 38 mm cap can carry a readable brand mark or product identifier, which is harder at 22 or 25 mm. Printing is laid out on flat sheet before forming, with distortion allowed for. The options are on the ROPP cap finishes page.
38 mm against the next size down
| 35 mm | 38 mm | |
|---|---|---|
| Typical fill | 150 ml to 500 ml | 200 ml to 1 litre |
| Typical use | Dry syrups, larger liquid packs | Wide-mouth bottles, powders, bulk packs |
| Typical aluminium | 0.22 to 0.24 mm | 0.23 to 0.25 mm |
| Typical carton | About 5,000 | About 4,000 |
Both suit wider necks. The choice usually follows the bottle already qualified for the product. The full range, from 22 mm upward, is on the pilfer-proof caps page.
Ordering 38mm ROPP caps
Printed 38 mm caps are quoted from artwork, so send vector artwork and its intended position on the crown with the bottle drawing, liner and colour. For a plain cap the drawing, liner and colour are enough.
Typical terms: standard designs from 50,000 pieces per colour, typically in 2 to 3 weeks from order confirmation; printed or custom-colour caps typically from 100,000 pieces in 4 to 6 weeks, since artwork approval comes first. These are confirmed with the quotation. Contact Autofits with your specification.
How this works in practice at Autofits
A printed 38 mm order goes through artwork approval before production, with the layout adjusted for the stretch the metal undergoes when the shell is drawn, so the mark reads correctly on the formed crown. Autofits has in-house design and development for this kind of custom work, and the caps are made with online high-speed camera inspection at the Nashik plant, which makes around 250 million aluminium pilfer-proof caps a month under ISO 15378:2017, ISO 9001:2015 and ISO 14001:2015 with Drug Master File 18100, as listed on the quality page.
Frequently asked questions
What bottle does a 38mm ROPP cap fit?
Wide-mouth glass or PET bottles with a 38 mm pilfer-proof screw neck, typically about 200 ml to 1 litre, used for the largest liquid packs and for powders and granules that are scooped out. The cap drawing is matched to your bottle drawing before a trial.
What is the largest ROPP cap size Autofits makes?
The largest pilfer-proof cap in the Autofits range is 38 mm. The range runs 22, 25, 28, 35 and 38 mm, all in AA8011 aluminium with EPE, latex or PVC liners and plain, printed or chamfered finishes.
Is a 38mm ROPP cap suitable for powders and granules?
Yes. The wide 38 mm neck lets powders and granules be filled without bridging and scooped out for dosing. Moisture ingress is the property to check, because a wide mouth has a longer sealing perimeter. The liner and the packaged system’s moisture barrier are confirmed during stability work.
Why is a 38mm ROPP cap thicker than a 22mm cap?
A wider cap spans a larger opening and forms a longer thread and pilfer band, so it is typically made from slightly heavier aluminium, around 0.23 to 0.25 mm against about 0.20 to 0.22 mm for small caps. The extra gauge resists crown dishing under top load and holds the threads firmly on a wide neck.
How many 38mm ROPP caps are in a carton?
About 4,000, the lowest typical count in the range because the 38 mm shell is the largest. Shell height and liner adjust it, and the count for your order is given in the quotation.
Related reading
- Pilfer-proof (ROPP) aluminium caps: the full range
- ROPP cap finishes: plain, printed and chamfered
- ROPP cap liners: EPE, latex and PVC
- Applying ROPP caps: roll-on capping and torque
- 35mm ROPP cap
- 28mm ROPP cap
- Pilfer-proof cap vs flip-off seal
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.*
