Glass Bottle Neck Finishes Explained

What a neck finish code actually means

A "neck finish" is the standardized shape and thread of a bottle's opening — it's what determines which cap, pump or dropper will actually fit. Most codes follow the GPI (Glass Packaging Institute) system: the first number is the finish's outer diameter in millimetres, and the second is a thread-series number. So 20/410 means a 20 mm diameter finish in the 410 thread series. The series number isn't a size — it's a thread pitch and profile family, and closures are only interchangeable within the same series.

Continuous-thread finishes

These are the screw-on finishes used for droppers, serums, lotions and most cosmetic bottles:

• 410 series (18/410, 20/410, 24/410) — the most common finish for dropper and treatment bottles
• 400 series (20/400, 24/400) — slightly different thread profile, common on pharmaceutical and lotion bottles
• 415 series (18/415, 20/415) — used for spray and mist pumps

A cap or pump made for 20/410 will not seal properly on a 20/400 bottle, even though both are "20 mm" — always match the full code, not just the diameter.

Lug finishes

Lug finishes use interrupted, cam-shaped threads instead of a continuous spiral, so a lid seats with a quarter-turn rather than several full turns. They're standard on food jars — you'll see codes like 43 mm lug or 63 mm lug on preserve, sauce and honey jars — because the quick-close action suits high-speed capping lines and vacuum-seal lids.

Crimp finishes

Crimp finishes are used almost exclusively for perfume and fragrance atomizers, where a metal collar is crimped onto a bead around the neck rather than threaded on. FEA 15 and FEA 13 (from the Fragrance Equipment Association's numbering) are the two you'll see quoted most; the number refers to the collar's inner diameter.

Pharmaceutical finishes

Pharma packaging tends to use its own finish standards: DIN 18 for dropper bottles, and PP 28 (poly-propylene 28 mm) for syrup and oral-liquid bottles taking child-resistant caps. Boston round bottles — the standard shape for tinctures and oral liquids — typically ship in 18, 20, 24 or 28 mm finishes.

Buyer tips

• Always test your actual closure — cap, pump or dropper — on a physical sample before committing to bulk production; small thread differences between mills can affect fit even at the "same" nominal size
• If you're switching suppliers on an existing product, send us your current bottle or its exact finish code rather than just a diameter
• Custom neck finishes are possible on new molds, but add development time and cost — stock finishes are almost always faster to launch with

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