Buyer Guide · Neck and Closure

How to Choose Bottle Neck Size: Diameter, Finish Code and Dispenser

Neck diameter is only half the specification. The finish code, the thread engagement and the dispenser have to agree with it — and they have to be settled before a tool is cut.

Quick answer

The neck is specified with its closure, never separately

A neck finish is defined by two things together: the diameter in millimetres and the thread finish code. Choosing the diameter alone is the single most common closure error we see in a brief.

The neck is also the most highly stressed part of the pack. It takes the torque every time the closure is opened and closed, it carries the thread the closure seals against, and it is the highest-precision feature on the bottle. A neck error found at sampling costs a tool; the same error found at the filler costs a shipment.

18–28 mm

Neck diameters in range

5 finishes

18/415 · 20/410 · 24/410 · 28/410 · 28/415

0.6–0.8 MPa

Assembled leak test

4 points

Wall thickness per cavity

5,000 pcs

MOQ, standard SKU

3–10 days

Sampling from a stock mold

Scope of this page

This guide covers the neck decision: what to specify, in what order, and what has to agree. The engineering detail of every finish code, thread form and closure family is on neck and closure.

Two numbers

Two numbers, and they do different jobs

A neck size alone tells you what will physically fit over the neck. It does not tell you what will seal. Confusing the two is how a pump and a bottle end up in the same shipment without working together.

	Neck size	Thread specification (finish code)
What it defines	The diameter in millimetres — 18, 20, 24 or 28.	The thread form, thread count and engagement length — 410 or 415.
How it is written	A stand-alone diameter.	The suffix in 24/410.
What it decides alone	What physically fits over the neck.	How the closure seals and how much wear the thread takes.
If you get it wrong	The closure will not go on.	The closure goes on and leaks, or loosens in use — the harder failure to find.

Two bottles can share a neck size and still need different closures. A closure specified for a 24/410 neck is not interchangeable with a 24/415 neck, because the thread engagement differs even though the diameter is the same.

The map

What each neck size is normally used for

Read the row your format sits in, then confirm the finish code against the closure you intend to fit. This is the working map we use when a brief arrives without a neck specified.

Neck	Finish codes we run	Closures normally fitted	Formats normally specified here
18 mm	18/415	Dropper, small screw cap, small mist sprayer.	Serum, essential oil, treatment and sample formats.
20 mm	20/410	Mist sprayer, small lotion pump, screw cap.	Facial mist, toner and small treatment formats.
24 mm	24/410	Lotion pump, disc-top cap, fine-mist sprayer, dropper.	Lotion, serum, cleanser and treatment formats — the most common neck we fit.
28 mm	28/410, 28/415	Larger lotion pump, foam pump, trigger sprayer, wide cap.	Shampoo, conditioner, body wash, hand wash and household cleaning.
Custom	On new tooling	Specified by the closure programme rather than by the standard range.	Programmes where the dispenser is fixed by an existing accessory or a filling line.

A larger neck takes a larger pump chamber, so a bigger neck means a bigger dose per actuation. 28 mm is normally chosen when the user needs a lot of product per press. An 18 mm neck on a large body is a frequent mistake: the pump cannot deliver enough per stroke for the volume, and the user pumps four times to get one application.

Selection order

Four questions settle the neck, and they are answered in this order

Answering them out of order is what produces a neck that has to be changed at sampling, which is the most expensive place to change it.

Start from viscosity, not from the bottle

Thin liquids suit mist sprayers and small necks. Lotions and gels need a lotion pump and a larger chamber. Pastes and creams usually need a wide-mouth jar and no neck at all.

Decide how the product is dispensed

Pour, press, spray, drip or squeeze. By the press means a pump, and a neck large enough for the chamber. By the drop means a dropper finish.

Check the dose against the pack size

Dose per actuation rises with the pump chamber, and the chamber is limited by the neck. This is the single most common reason a 24 mm neck is upgraded to 28 mm during sampling.

Check how often the pack is opened

A format opened and closed repeatedly benefits from a longer thread engagement and a hinged or tethered closure, because the neck takes the wear. That is the difference between a 410 and a 415 finish at the same diameter.

If the closure already exists because your brand supplies it, the last question becomes the first: the neck follows the closure. Send us a physical closure sample and we will identify the finish it needs and confirm it against the bottle neck before tooling.

The assembly

Neck and closure are one assembly, and five interfaces have to agree

Fit and leak failures happen at the interface, not in either part alone. That is why we test the assembled unit rather than the bottle, and why the neck is never confirmed in isolation.

Checklist

The five interfaces to confirm before tooling

Neck and closure interface

☐Neck diameter and finish code must both match the closure. A 24/410 pump on a 24/415 neck is not a match.
☐The sealing mechanism — plug seal, liner or cone — must suit the neck land geometry.

Dispenser geometry

☐Dip tube length and cut angle, set against the bottle height and the base profile.
☐Dose per actuation against the pack size, so the pack delivers the number of applications the label claims.

Assembly in production

☐Application and removal torque measured on the assembled unit, against the window agreed for that bottle and closure pair.
☐An air-pressure leak test at 0.6–0.8 MPa with the unit inverted and held, accepting zero leakage on the assembled pack.

All five are covered in the neck and closure engineering page, and the dispenser side is worked through in full in how to match a pump with a bottle.

Precision

Why the neck is the highest-precision feature on the bottle

The neck carries the thread the closure seals against, and it is the interface between two parts made by different processes. Everything else on the bottle is judged visually; the neck is judged by whether the pack leaks.

What that means in practice

▸The neck is checked against your actual cap, pump or sprayer rather than against a nominal gauge, because the closure is what has to fit.
▸Neck finish and thread fit are verified in process, not only at the end of the run, so a drift is caught while it is still correctable.

▸The leak test runs on the assembled bottle plus closure, because testing the bottle alone would not prove anything about the pack the user receives.
▸Where a closure sample exists, send it: a physical closure tells us more than a drawing, and it can be measured rather than interpreted.

A neck mismatch discovered at sampling costs a tool. The same mismatch discovered at the filling line costs a shipment, because the bottles are already made and the packs cannot be closed.

Limits

When a standard finish will not do

The stock range covers 18/415, 20/410, 24/410, 28/410 and 28/415. Outside that, the neck becomes a tooling decision rather than a catalogue choice.

Situation	What it usually means	What it costs
The closure is a non-standard accessory you already own	The neck is cut to the closure, which normally means new tooling or a neck insert on a stock tool.	A tooling intervention, quoted per project, and a sampling round to prove the fit.
The format needs a dose no standard chamber delivers	A larger neck, a different pump family, or a two-stage dispenser.	A neck change first, which may pull the capacity and the closure with it.
The pack has to accept a tamper-evident or child-resistant closure	The finish and the neck land are part of the closure system rather than a bottle choice.	Settled with the closure supplier before tooling, not after.
The market requires a specific closure interface	The finish is fixed by the requirement rather than by preference.	A stock finish may still work; if not, tooling is the honest answer.

Where a custom finish is needed, the neck is designed with the closure rather than around it, and the fit is proved on the assembled unit before production is released.

Mistakes

The five neck mistakes that cost the most

Seen often enough to list

▸Specifying the diameter and leaving the finish code to the factory. The factory will fit what it has, which may not be what your closure needs.
▸Choosing the neck before the dispenser. The neck is limited by the closure, not the other way round.
▸Upgrading the neck without re-checking the capacity. A larger neck changes the shoulder and the usable volume, and the label claim may move with it.
▸Assuming a 410 and a 415 finish are interchangeable at the same diameter. They are not; the thread engagement differs, which is exactly what the code describes.
▸Leaving the neck open until sampling. The neck is the part a tool is cut around, and an open neck finish means the closure has to be settled before the tool can be finished.

Next step

Send us the closure and we will confirm the neck

▸The neck diameter you have specified, or the bottle you are matching.
▸The finish code, or the closure itself — a physical sample is best.
▸What the pack holds, and its viscosity, so the dose can be checked against the neck.
▸The dose per application the label will claim.
▸Whether the closure is supplied by you or sourced as a matched assembly.
▸The bottle capacity and height, if they are already fixed.

A physical closure sample tells us more than a drawing. Where you cannot supply one, send the finish code and we will confirm what is available against the shape and capacity you need.

Neck, closure and dispenser reading

Other buyer guides

Sourcing plastic bottles from China →Buying custom plastic bottles →Stock mold vs custom mold →Choosing bottle capacity →Matching a pump to a bottle →Requesting a packaging quote →Plastic bottle sampling →

Engineering and manufacturing detail

Bottle design →Neck and closure →Formula compatibility →Decoration →Color matching →Packaging testing →Material comparison →Injection molding →ISBM — stretch blow →EBM — extrusion blow →

Deeper reading

Bottle neck finishes 24/410 vs 28/410 →Bottle neck finishes explained: 18 / 20 / 24 / 28 mm →Lotion pump bottles: pumps, output and dose →Airless pump bottles: complete buyer guide →Mist and atomizer spray bottles →Buy caps and pumps from the bottle supplier? →

Formats and products

Buyer Guides hub →Cosmetic bottles →Dropper bottles →Lotion bottles →Pump bottles →Neck and closure engineering →

FAQ

Bottle neck and closure questions

What does 24/410 mean?+

The 24 is the neck diameter in millimetres, which is the outside diameter the closure grips. The 410 is the thread finish code: the standard single-turn screw finish used across 24 mm and 28 mm necks, and the most common lotion-pump interface we fit.

What does 28/410 mean?+

A 28 mm neck diameter with the same 410 single-turn finish code. It takes the larger lotion pumps, trigger sprayers and foam pumps, and it is the usual interface for shampoo, body wash and cleaning formats.

Will a 24/410 pump fit a 24/415 bottle?+

Not reliably. The diameter matches but the thread engagement does not, so the closure may cross-thread, leak or loosen in use. Match the finish code as well as the diameter, and where you cannot, send us the closure and we will confirm the neck finish the bottle has to be made with.

What neck finishes do you run?+

The range covers 18/415, 20/410, 24/410, 28/410 and 28/415, with custom finishes on new tooling. Send us the closure or the finish code and we will confirm what is available against the shape and capacity you need.

How do I choose a bottle neck size?+

Work through four questions in order: viscosity of the product, how it is dispensed, whether the dose per actuation fits the pack volume, and how often the pack is opened and closed. If the closure already exists, the neck follows the closure instead.

Why does the neck matter more than the rest of the bottle?+

It is the most highly stressed part of the pack and the highest-precision feature on the part. It carries the thread the closure seals against, and it is the interface between two parts made by different processes, so any error shows up as a leak rather than as a cosmetic defect.

Do you test the neck and closure together or separately?+

Together. Neck finish and thread fit are checked against your actual cap, pump or sprayer rather than a nominal gauge, application and removal torque are measured on the assembled unit, and an air-pressure leak test runs at 0.6–0.8 MPa with the unit inverted and held. Zero leakage on the assembled pack is the acceptance criterion.

Can you match a neck to a closure I already own?+

Yes. Send a physical closure sample and we will identify the finish it needs and confirm it against the bottle neck before tooling. Where no stock finish matches, the neck becomes a tooling decision and is quoted with the tool rather than after it.

Send the closure and we will confirm the neck

A physical closure sample tells us more than a drawing. Tell us what the pack holds and how it is dispensed, and we will come back with the neck finishes that work and the tooling position if none of them does.

Talk to Engineering Request a Quote

Part of Buyer Guides: Sourcing, Specifying and Ordering Packaging | Shijin

Keep reading

Material, engineering and buying pages that this one sits next to.

How to Buy Custom Plastic Bottles: Four Levels of Custom | Shijin How to Choose Bottle Capacity: Fill Volume and Headspace | Shijin How to Evaluate a Plastic Packaging Supplier | Shijin How to Match a Pump to a Bottle: Five Interfaces | Shijin How to Request a Plastic Packaging Quote: 14-Item Brief | Shijin How to Source Plastic Bottles from China: Buyer Guide | Shijin Plastic Packaging Materials: PET, HDPE, PE, PETG, PP and PCR | Shijin

Products behind this page

Real items from the Shijin stock-mold library. Shown specifications are the published ones; a quotation is built from your own drawing and fill volume.

PET | 15 ml | SJT0484-15-05