Quick answer: A bottle neck finish is the measured thread and neck geometry of a container, written as two numbers — the neck diameter in millimetres, followed by a thread code. In 20/410, “20” is the 20 mm neck diameter (the T dimension) and “410” is a continuous-thread finish; 24/410 is the same thread style on a wider 24 mm neck. Your closure must match both numbers. Match only the diameter and the cap will cross-thread, leak or loosen in transit.
Closures are no longer a commodity line item. Global Market Insights values the global caps and closures market at USD 81.8 billion in 2025, forecast to reach USD 132.7 billion by 2035 at a 4.8% CAGR — growth driven by engineered dispensing systems rather than basic screw caps. This guide explains how to specify a neck finish correctly for custom cosmetic bottles, so your caps, droppers and pumps fit and seal the first time.
What Is a Bottle Neck Finish and How Do You Read a GPI Code?
The bottle neck finish is the complete spec of the opening: outside thread diameter, number of thread turns, inside neck diameter, orifice and thread start height. The Glass Packaging Institute (GPI) system standardised this into a short code any supplier can read — which is why buyers quote a bottle neck finish in RFQs instead of describing caps in words.
Take 24/410 as an example. The first figure is the thread diameter in millimetres — 24 mm. The second figure describes the thread style: the 400/410 series is a continuous thread (CT) finish used with standard screw caps, while 415 denotes a deeper, longer thread that gives extra engagement for heavier closures and closures that will be re-opened many times. The GPI system is supported by SPI plastic-thread standards so that a cap from one supplier fits a bottle from another — as long as both sides quote the same finish.
Three numbers to remember
- First number = neck diameter in mm (18, 20, 24, 28…)
- 400 / 410 / 430 = continuous thread — standard screw caps and CT closures
- 415 = deeper thread — more turns, better grip for heavy or frequently opened closures
GPI standards are the reference US and EU buyers quote in purchase orders, and they are why a 20/410 cap is not interchangeable with a 20/415 cap even though both diameters look identical on a drawing.
Bottle Neck Finish Chart: Common Sizes for Cosmetic Bottles
Cosmetic packaging clusters around a small number of neck finishes. The chart below covers the bottle neck finish sizes you will see on custom glass bottles, plastic bottles and jars, with the closures and products each one normally carries.
| Bottle neck finish | Neck diameter | Thread type | Typical closures | Typical cosmetic use |
|---|---|---|---|---|
| 18/400 | 18 mm | Continuous thread | Droppers, orifice reducers, roller balls | Essential oils, 5–10 ml perfume samples, serums |
| 18/415 | 18 mm | Deeper thread (2.0 turns) | Droppers, aluminium caps, fine mist sprayers | Fragrance samples, travel serums, alcohol-based liquids |
| 20/410 | 20 mm | Continuous thread (1.5 turns) | Small screw caps, treatment pumps, disc tops | Sample and travel sizes, facial oils, 1–4 oz bottles |
| 24/410 | 24 mm | Continuous thread (1.5 turns) | Lotion pumps, disc tops, flip tops, screw caps | Lotions, micellar water, cleansers, 100–500 ml bottles |
| 24/415 | 24 mm | Deeper thread (2.0 turns) | Heavy duty pumps, tamper-evident closures | Body care, refillable formats, larger 250 ml+ bottles |
| 28/410 | 28 mm | Continuous thread | Lotion pumps, sprayers, trigger caps | Shampoo, body wash, 250 ml–1 L containers |
Neck finish standards and compatible closures per the Alibaba.com glass bottle attribute and closure guide; dimensional values cross-checked against GCMI thread-finish data.
If you need the actual dimensions rather than the nominal code, the three most common cosmetic finishes measure as follows:
| Dimension | 18/415 | 20/410 | 24/410 | Target tolerance |
|---|---|---|---|---|
| T — thread diameter (mm) | 18.0 | 20.0 | 24.0 | ±0.2 mm |
| Thread style | 415 (2.0 turns) | 410 (1.5 turns) | 410 (1.5 turns) | — |
| E — inside neck diameter (mm) | 13.0 | 15.0 | 18.5 | ±0.3 mm |
| I — inner orifice (mm) | 11.5 | 13.0 | 16.0 | ±0.2 mm |
| S — thread start (mm) | 2.5 | 2.7 | 3.2 | ±0.2 mm |
Dimensional data per published GCMI thread finish standards for 18/415, 20/410 and 24/410.
How to Measure a Bottle Neck Finish Before Ordering Caps
Suppliers publish the bottle neck finish, but verifying it on a physical sample takes five minutes and prevents a whole batch of unusable caps. Work in this order:
- Measure the thread diameter (T). Use digital callipers across the outside of the threads, not the smooth neck below them. A 20 mm finish measures 20.0 mm ±0.2 mm; a reading of 23.5 mm on a “24 mm” bottle is within spec, but 22 mm is not.
- Count the thread turns. This is what separates 410 from 415. A 24/410 neck shows roughly 1.5 turns; a 24/415 shows two full turns. The difference is visible with the naked eye and is the most common reason a 24/410 cap will not sit flush on a 24/415 bottle.
- Check the inside neck diameter (E) and orifice (I). These decide which dropper, reducer or pump stem will fit — a 13 mm inside neck accepts a different dropper than an 18.5 mm one.
- Confirm where the thread starts (S). If the thread start is too high, the cap bottoms out on the shoulder before the liner compresses, and the bottle leaks even though it feels tight.
- Approve a physical cap sample. Never approve a closure from a drawing alone. Ask for a filled sample bottle and check it inverted, shaken and in transit before you commit to the order quantity.
One practical warning: the “20 mm” in a bottle neck finish is the thread diameter, not the cap diameter or the bottle width. Buyers regularly order 20 mm caps for 18/415 bottles assuming the two are close enough. That 2 mm gap is one of the most frequent causes of mismatched orders we see.
Matching Closures to Your Bottle Neck Finish: Droppers, Pumps, Sprayers and Disc Tops
Once the bottle neck finish is confirmed, closure selection is mostly about formulation and usage. The table maps the usual combinations.
| Closure type | Common neck finishes | Best for | Example |
|---|---|---|---|
| Glass or plastic dropper | 18/400, 18/415, 20/410 | Serums, facial oils, essential oils — accurate dosing | 30 ml straight round glass serum bottle |
| Fine mist sprayer | 18/415, 20/410 | Perfume, toner mist, fragrance samples | 10 ml slim glass perfume sample bottle |
| Airless pump | Threaded collar, 20/410 and above | Retinol and vitamin C formulations with no preservatives | 20–50 ml square airless pump bottle |
| Lotion pump | 24/410, 28/410 | Lotions, cleansers, body care in 100–500 ml | Airless bottle range |
| Brush cap or wand | 13/415-style nail polish finishes | Nail polish, lip gloss, mascara | 13 ml teardrop nail polish bottle |
| Disc top or flip top | 20/410, 24/410 | Shampoo, micellar water, one-handed dispensing | Glass bottle collection |
For fragrance specifically, sample and travel formats sit on narrow finishes such as 18/415 and 20/410 — see our perfume bottle range for the spray and crimp options available on those necks.
Cap Torque and Leak Testing: The Spec Most Buyers Forget
A neck finish and a closure can be dimensionally perfect and still leak, because sealing also depends on how tightly the cap is applied. Cap torque — measured in newton-metres (Nm) — controls that, and it is the spec most often missing from cosmetic packaging orders.
| Torque applied | Result | Suitable for |
|---|---|---|
| Below 0.6 Nm | Under-torqued; loosening risk in vibration | Never use for alcohol-based formulas |
| 0.6–0.8 Nm | Marginal seal; shipping risk | Oil-only formulations |
| 0.8–1.0 Nm | Correct low end of the engineering window | Alcohol-based product with a PE liner |
| 1.0–1.2 Nm | Correct high end; best seal security | Alcohol-based product with a PTFE-faced liner |
| Above 1.2 Nm | Over-torqued; liner distortion, cracking risk | Never use on glass bottles |
Torque window per published GCMI thread finish and leak-proof seal validation data for glass containers.
A workable quality protocol takes three steps. Set the capping head to 1.0 Nm, the centre of the validated window, using a calibrated torque head rather than operator judgement. Run an inverted storage test: fill bottles, cap them, store them upside down at 40 °C for 14 days and inspect for weeping at the thread. Then add a transport simulation, because vibration — not temperature — is what loosens under-torqued caps in e-commerce parcels.
Liner material matters as much as torque. Polyethylene (PE) liners suit most cosmetic formulations, while alcohol-based products such as fragrance and toners need a PTFE-faced or polycone liner, since alcohol attacks ordinary liner materials over time.
Bottle Neck Finish Mistakes That Cause Leaks, Returns and Reorders
- Treating 400, 410 and 415 as interchangeable. Diameter may match; thread depth does not, so the cap never reaches the sealing surface.
- Confusing cap diameter with neck diameter. A “20 mm cap” refers to a 20 mm thread finish, not the cap’s outer width.
- Skipping the liner specification. Omitting liner material from the purchase order is the fastest route to leaks in alcohol-based products.
- Approving closures without a filled sample. Drawings hide thread-start height and moulding flash; a filled, inverted sample exposes both.
- Leaving bottle neck finish off the PO. Order a “30 ml glass bottle” with no finish quoted and the factory will choose one for you — possibly not the one your existing caps fit.
- Changing cap supplier without re-verifying. Cross-supplier compatibility holds only when both sides quote the same GPI finish at the same tolerance.
What Is Driving Closure Engineering in 2026
Closure selection is becoming a strategic decision rather than an accessory purchase. According to Global Market Insights’ caps and closures market report (June 2026), the market moves from USD 81.8 billion in 2025 to a projected USD 132.7 billion in 2035 at a 4.8% CAGR. Screw closures represent USD 31.4 billion (38% share) and grow faster than average at 5.2%, while plastic closures hold 79% of value at USD 65.1 billion, led by polypropylene for its chemical resistance and moulding performance.
Market snapshot — caps and closures
- USD 81.8 bn in 2025, forecast to USD 132.7 bn by 2035 (4.8% CAGR)
- USD 31.4 bn / 38% share — screw closures, growing at 5.2%
- 79% share / USD 65.1 bn — plastic closures, predominantly polypropylene
- 90% of global glass production is Type III soda-lime glass — the standard substrate for cosmetic bottles
The report’s central finding is structural: growth is shifting from commodity sealing products toward engineered closure systems built for specific end uses — dispensing closures, precision dosing and functional caps. For brands, the closure is now part of the product experience rather than a line item to minimise. For buyers, it means the bottle neck finish conversation must happen before the bottle is tooled, not after.
How to Specify Bottle Neck Finish in Your Next RFQ
Send these six data points with your enquiry and a packaging manufacturer can quote accurately on the first pass:
- Bottle neck finish code for bottle and cap (for example 24/410, not “24 mm”)
- Closure type and material — pump, dropper, sprayer, disc top or screw cap
- Liner material if the formulation contains alcohol or essential oils
- Target fill volume and product viscosity
- Required cap torque window for your filling line
- Whether the item must survive e-commerce shipping, and any transit test standard you follow
Lansenpack produces custom glass and plastic cosmetic packaging with matched closures across the common GPI finishes, including glass bottles, perfume bottles and airless formats. Every development order includes a filled, capped sample for torque and leak verification before mass production.
Need more context on sizes, materials and order quantities first? Read the Lansenpack packaging blog for our guides on bottle selection and customisation.