There is a detail in the design of a container that goes unnoticed until something goes wrong: the thread. That finish on the neck where the closure screws on is not a secondary element. It determines whether the cap seals properly, if there are leaks, if the dosing system works, and if the whole assembly complies with the applicable regulations.
And here is the most common mistake: assuming that two containers with the same neck diameter are interchangeable. They are not. A 28-410 thread and a PP28 may measure the same at first glance, but they have different heights and thread pitches. Using the wrong closure can cost an entire batch.
In cosmetics, pharmacy, and laboratory, three thread types cover the vast majority of use cases: DIN18, PP28, and GL45. Knowing them well saves problems.
DIN18: the thread of the dropper
If you work with essential oils, serums, or any liquid formula that is dosed drop by drop, you already know this thread, even if you don't know its name.
DIN18 —which also appears as GL18 in some catalogs, both for the same dimensional range of 18 mm— is the dominant standard in Europe for bottles from 5 to 200 ml that use pressure seals or dropper pipettes. The finish is specifically designed for that type of precise and controlled dosing.
- Common closures: threaded caps with tamper-evident seal (TE), dropper stopper, pipette, and specific sprays or dosing pumps for 18 mm.
- When to choose it: essential oils, serums, extracts, and any low-viscosity liquid formula where dose control is important. If the product is going to retail, add a TE seal.
A practical note: if you see GL18 in a supplier's catalog, always ask for the dimensional drawing. In practice, they are used as equivalents, but it's advisable to confirm it.
PP28: the cap of syrups and liquid orals
The PP28 is the standard in pharmacy for formats ranging from 100 to 1,000 ml. Its uniqueness lies in the type of closure it uses: ROPP (Roll-On Pilfer Proof) caps, which are formed over the thread during the capping process, creating an integrated tamper-evident band.
There are CRC (child-resistant) versions for products that require them, and some models include dosing cups, which is common in pediatric syrups.
- Common closures: ROPP TE aluminum or plastic caps, with or without CRC, and dosing cups according to the application.
- When to choose it: syrups, oral solutions, nutraceuticals, and any product that requires a tamper-evident band and, if applicable, child protection. Also available in PET bottles with a PP28 neck for certain pharmaceutical ranges.
Attention: PP28 and 28-410 are not the same and are not compatible. They have different heights and thread pitches. It is one of the most common compatibility errors in technical purchases.
GL45: the universal language of the laboratory
If DIN18 is the thread for cosmetics and PP28 is for pharmacy, GL45 is the thread for the laboratory.
Defined by the ISO 4796-1 standard, the GL45 is the standard for reagent bottles ranging from 25 ml to 20 liters. Its 45 mm neck allows for high flow, and there is a whole family of accessories around it: PP or PBT caps for high temperature, pouring rings, vented stoppers, HPLC connectors, pass-throughs... It is a system, not just a thread.
- Common closures: GL45 threaded caps in PP or PBT with PTFE or silicone gaskets, pouring ring, and accessories for connection to equipment.
- When to choose it: storage of reagents, culture media, feeding of instruments. For applications with high temperature or chemical demands, opt for PBT caps with PTFE/silicone liners and ETFE pouring rings.
The GL45 borosilicate bottles are autoclavable, but the cap must be compatible with that temperature. Not all of them are.
Technical comparison
| Criterion | DIN18 | PP28 | GL45 |
|---|---|---|---|
Nominal diameter | 18 mm | 28 mm | 45 mm |
| Typical format | 5–200 ml | 100–1000 ml | 25 ml–20 L |
| Security | Seal TE | Inviolable (ROPP/TE) | Sturdy lids + accessories |
| Dosing | Drop by drop (insert) | Controlled discharge | Spill, pumps, probes |
| Sections | Cosmetics | Pharma, food/care, cosmetics | Laboratory |
Sources and compatibility guides: thecarycompany.comrichmondgroup.comISO
The most common error
Choosing the thread based on diameter without verifying the thread profile. In B2B purchases, this mistake can result in a batch of incompatible closures, leaks in the filling line, or a non-conformity in an audit.
The way to avoid it is simple: identify the thread standard from the beginning of the process, always request the dimensional drawings from the supplier, and verify the compatibility of the complete set —container, thread, closure, and liner— before finalizing the order.
In summary
- DIN18 → precision cosmetics, drop-by-drop dosing
- PP28 → pharmacy and nutraceuticals, tamper-evident band ROPP
- GL45 → laboratory, ISO 4796-1, complete accessory system
Three threads, three well-defined contexts of use. Knowing them prevents most compatibility issues that arise after purchase.
Do you need help identifying the right thread and closure for your application?
At Comercial Labor, we have DIN18, PP28, and GL45 bottles with their compatible closure sets, technical specifications, and traceability.
Bibliography
ISO 4796-1:2016 · DWK Life Sciences (DURAN®) · Fisher Scientific · Richmond Group · The Cary Company · Miron · Gerresheimer · Amcor / Modulpac · LABComercial