Engineering · Neck & Closure

Neck and Closure: Sizes, Threads and How to Match a Pump to a Bottle

18 mm to 28 mm necks, what 24/410 and 28/410 actually mean, and why the neck and the closure are one assembly rather than two parts.

Quick answer

The neck is the most highly stressed part of the pack, so it is specified with its closure, never separately

A neck finish is defined by two things together: the neck diameter (18, 20, 24 or 28 mm in the formats we run most) and the thread finish code that describes the thread form and how many turns it engages. Matching the diameter is not enough. 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.

Our range covers the neck finishes 18/415, 20/410, 24/410, 28/410 and 28/415, with custom finishes on new tooling. Caps, closures, lotion pumps, foam pumps, mist and trigger sprayers and droppers are all matched to the bottle neck and tested as an assembled unit, because leak and fit failures happen at the interface, not in either part alone.

18–38 mm

Neck finishes in range

24/410

Most common lotion neck

28/410

Most common large neck

18/415

Classic dropper finish

0.6–0.8 MPa

Leak test pressure

Assembled

Closure test basis

Neck sizes

Bottle neck sizes and what each one is normally used for

The diameter decides what can be mounted on the bottle, the dose a pump can deliver, and how much product the user can get out of the pack. The table below is the working map we use when a brief arrives without a neck specified.

Neck size	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, mist sprayer, screw cap, flip top	Lotion, hand wash, sanitising gel and general personal care
28 mm	28/410, 28/415	Lotion pump, trigger sprayer, foam pump, screw cap, flip top	Shampoo, body wash, cleaning sprays and larger-dose formats
Custom	On new tooling	Per the closure specified	Formats where the dispenser or the cartridge dictates the interface

Two practical rules sit behind that table. 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. And 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.

The codes

What 24/410 means, and what 28/410 means

The two numbers do different jobs, and confusing them is the single most common closure error we see in a brief.

Reading a neck finish code

24/410

The 24 is the neck diameter in millimetres — 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. It is the most common lotion-pump finish we fit, and the one a buyer is most likely to receive when they specify a 24 mm neck without naming a code.

28/410

The 28 is the neck diameter in millimetres; 410 is the same single-turn finish code. A 28/410 neck takes the larger pumps, trigger sprayers and foam pumps, and is the usual interface for shampoo, body wash and cleaning formats.

18/415

An 18 mm neck with a 415 finish — the classic dropper and essential-oil interface. The longer thread engagement of a 415 finish suits the smaller diameter and the repeated opening and closing a dropper bottle gets.

28/415

A 28 mm neck with a 415 finish: the same diameter as 28/410 but a longer thread engagement, used where the closure is heavier or opened and closed more often.

Why the code matters

Diameter alone does not define the interface. The finish code defines thread form, thread count and engagement length. A closure designed for one finish will not seal reliably on the other, even at the same diameter — and the failure usually appears as weeping or cross-threading rather than as an obvious misfit.

The finish designation is a standard, not a supplier preference. That is what makes it useful: it lets a closure be sourced independently of the bottle and still fit. But standards only work if both sides are specified, which is why we ask for the finish code and, where possible, a physical closure sample.

Closure families

Screw cap, pump, sprayer, dropper, trigger, flip top and foamer

Each family solves a different dispensing problem, and each one constrains the neck it can mount on.

Shampoo, body wash, gels and any format dispensed without a separate cap to lose

Closure	What it is	Typical neck	Formats it is used on
Screw cap	A plain threaded closure, with or without a sealing liner, opened by hand	18 mm to 28 mm	Anything the user pours or dips into; the simplest and lowest-cost closure
Lotion pump	A spring-loaded pump with a dip tube, delivering a metered dose per press	24/410 and 28/410	Lotion, hand wash, body wash, sanitising gel — anything dispensed by the dose
Mist sprayer	A fine-output finger sprayer for low-viscosity liquids	18 mm to 24 mm	Facial mist, toner, setting spray, sanitiser; output rate is set by the pump, not the bottle
Dropper	A pipette or dropper insert, usually under a screw cap	18/415	Serum, essential oil and treatment formats where the dose is measured in drops
Trigger	A hand-operated trigger sprayer with a nozzle, for larger volumes	28/410	Cleaning sprays and household formats where the user covers an area rather than a dose
Flip top	A hinged lid over a dispensing orifice, opened one-handed	24 mm and 28 mm	Shampoo, body wash, gels and any format dispensed without a separate cap to lose
Snap-on	A press-on closure that snaps over a bead on the neck, opened by pull or lift, with no thread engagement	18 mm to 28 mm	Samples, trial-size bottles and sachet-top formats where the pack is opened once or only a few times
Foamer	A pump that mixes liquid with air to produce foam at the nozzle	28 mm and up	Hand soap, facial cleanser and shampoos formulated as foam; the formula has to be designed for foaming

Closure function is a specification item, not an accessory. Dose per actuation, spray pattern and output rate are user-experience parameters, and they are agreed and then checked on the assembled unit.

Matching

How to match a pump with a bottle

A pump and a bottle match on five separate interfaces. All five have to agree, which is why we test the assembly rather than the parts.

Neck diameter and finish code

Confirm that the pump’s stated finish matches the bottle neck exactly — diameter and code. A 24/410 pump on a 24/415 neck is not a match.

Thread engagement and sealing

Check that the pump seals on the neck land without cross-threading, and that the sealing mechanism — plug seal, liner or cone — suits the neck geometry.

Dip tube length and cut angle

The tube is cut to the internal height minus the pump. Too long and it sits on the base and the pack will not empty; too short and the last 10–15% of the fill is unreachable.

Dose per actuation against pack size

Work out the doses per pack the user experience needs. A pump that under-delivers for the volume forces repeat pressing, which reads as a poor product.

Fit, torque and leak on the assembled unit

Test application and removal torque, then air-pressure leak test at 0.6–0.8 MPa, inverted and held, on the assembled bottle plus closure. Zero leakage is the acceptance criterion.

Do this before tooling. A neck mismatch discovered at sampling costs a tool; the same mismatch discovered at the filler costs a shipment.

Choosing

How to choose bottle neck size

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

Neck selection rules

1. How viscous is the product?

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.

2. How is the product dosed?

By the drop means a dropper and an 18 mm finish. By the press means a pump, and a neck large enough for the chamber. By the area covered means a trigger and a 28 mm finish. For a measured pour, a screw cap with a controlled orifice.

3. How much per dose?

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.

4. What does the user do between uses?

A format opened and closed repeatedly benefits from a longer thread engagement and a hinged or tethered closure, because the neck takes the wear.

Where the closure already exists because the customer supplies it, 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 distinction

Neck size versus thread specification

These two terms are used interchangeably in conversation and they are not the same thing, which is how closures get ordered wrongly.

	Neck size	Thread specification (the finish code)
What it defines	The diameter in millimetres — 18, 20, 24, 28	The thread form, thread count and engagement length — 410, 415
Example	24 mm	410
Written as	A stand-alone diameter	The suffix in 24/410
What it alone decides	What physically fits over the neck	How the closure engages and seals
Can two bottles share a neck size and not share closures?	Yes	Yes — and this is the failure mode
What to send us	The diameter you have specified, or your existing bottle	The finish code, or the closure itself

The practical version: neck size tells you what will fit, thread specification tells you what will seal. Specify both, and if you only have one, send the closure.

Neck and closure: buyer 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.

How do I match a pump with a bottle?+

Five interfaces have to agree: neck diameter, finish code, the sealing mechanism and its seat on the neck land, dip tube length and cut angle, and the dose per actuation against the pack size. Then test the assembled unit for application and removal torque and for leakage. We air-pressure leak test the assembly at 0.6–0.8 MPa, inverted and held, and accept zero leakage.

How do I choose a bottle neck size?+

Start from viscosity: thin liquids take mist sprayers and small necks, lotions and gels take a lotion pump, pastes take a wide-mouth jar. Then work through how the product is dosed, how much per dose, and what the user does between uses. Dose per actuation is limited by the neck, and that is the usual reason a neck is upgraded during sampling.

What is the difference between neck size and thread specification?+

Neck size is the diameter in millimetres — 18, 20, 24 or 28. The thread specification is the finish code, such as 410 or 415, and it defines the thread form, thread count and engagement length. Neck size tells you what will fit; thread specification tells you what will seal. Two bottles can share a neck size and still need different closures.

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 or weep rather than seat. 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 you make sure a closure does not leak?+

Fit and leak behaviour are tested on the assembled unit rather than on the bottle alone: neck finish and thread fit checked against your cap, pump or sprayer, closure torque measured, then an air-pressure leak test at 0.6–0.8 MPa with the unit inverted and held. Zero leakage is the acceptance criterion, and the results go in the QC report for the lot.

On this page

Necks and closures we support

Neck and closure options covered here include 24/410 bottle neck, 28/410 closure, 18/415 dropper neck and 20/410 neck size, plus snap on cap bottles, trigger sprayer bottle and foam pump bottle neck for samples and production runs.

Send us the closure and we will confirm the neck

A physical closure sample tells us more than a drawing. Send one with the capacity and the material, and we will come back with the neck finish, the bottle that fits it and the assembly test result.

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Part of Packaging Engineering: Bottles, Closures and Decoration | Shijin

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