Cosmetic Bottle Neck Finishes: A Buyer's Specification Guide

Every bottle, pump, sprayer, dropper and cap in a beauty range has to agree on one thing: the neck finish. Get it right and components from different production runs — and different suppliers — fit, seal and dispense the same way. Get it wrong and a pump wobbles, a dropper leaks in transit, or a cap that looked right at the sample stage never quite tightens. This guide explains the code, the dimensions behind it, and how to verify a match before you commit to a wholesale order.

How to Read a Neck Finish Code

Most screw-thread finishes on cosmetic bottles and jars follow a system set by the Glass Packaging Institute (GPI) and the Society of the Plastics Industry (SPI). The code is two numbers separated by a slash, such as 24/410 or 28/410.

The first number is the nominal thread diameter in millimeters — the outside diameter measured across the threads. It is not the size of the opening. The second number is the thread style, or finish series, a standardized profile that controls how many turns the thread makes and how tall the neck is. So 24/410 means a finish about 24 mm across the threads with roughly one and a half turns of thread — the workhorse profile for lotion pumps, disc-top caps and fine-mist sprayers.

This is the single most common mistake first-time buyers make: they match only the millimeter size and ignore the series. Two bottles can both be "24 mm" yet carry different thread profiles, and a closure made for one style may thread on partway and then stop, never sealing as designed.

The Five Dimensions Behind the Code

Behind every finish code are five measurements that closure makers design to. On a technical drawing they appear as the letters T, E, I, H and S:

• T — outside diameter of the thread (gives the code its first number).
• E — outside diameter of the neck just below the threads. Thread depth is half the difference between T and E.
• I — inside diameter of the neck (the bore). This must clear your filling nozzles, dip tubes and orifice inserts.
• H — height of the finish, from the top of the neck down to where the T diameter meets the shoulder.
• S — distance from the top of the finish to the top edge of the first thread; it decides how far the closure seats and how much thread it grips.

In day-to-day sourcing you will quote T and the series. You reach for E, I, H and S only when something goes wrong — a pump that bottoms out on the shoulder, a nozzle that will not enter the bore, or a cap that backs off after capping.

Thread Series: 400, 410 and 415

The three styles you will meet most often in cosmetics differ in how many turns the thread makes, and therefore in how tall the neck is:

• 400 — one turn, the shortest finish. Used across a wide range of sizes, from 18 mm dropper bottles to 89 mm jars. Typical on Boston rounds and standard screw-cap jars.
• 410 — about one and a half turns, a medium-height finish in the 18–28 mm range where pumps and sprayers need a secure, upright fit. The default for treatment pumps, lotion pumps and fine-mist sprayers.
• 415 — two turns with a taller neck. Used on some premium fragrance and cosmetic bottles that need deeper thread engagement, and on selected child-resistant or tamper-evident closures.

Other series exist — 425 and 430 (buttress) and lug finishes such as 2030 — but their definitions vary between suppliers' charts. For anything outside 400, 410 and 415, work from the closure maker's actual drawing.

Common Cosmetic Neck Finishes

The table below lists finishes you will routinely see quoted for wholesale beauty and personal-care packaging:

Always confirm the specific bore and thread profile on the component you intend to pair. Our cosmetic closures guide covers liner chemistry and cap families that pair with these finishes.

Why Matching Both Numbers Prevents Leaks

A 24/410 closure is too small for a 28/410 bottle — the diameters differ by 4 mm and the threads never engage. The subtler failure is a 24/400 cap on a 24/410 bottle: the first number matches, but the finish series does not. The cap may begin to thread and still fail to seat, compress its liner, cover the neck correctly, or retain torque. That mismatch is the classic cause of leaking orders and failed leak tests. A finish designation is the starting interface specification; the complete package still depends on the sealing system, material tolerances, application torque and your filling process.

Beyond GPI/SPI: DIN, FEA and Proprietary Airless

GPI/SPI dominates North American plastic and glass packaging, but it is not the only system. Europe leans on the DIN standard (DIN 18, 20, 24, 28, 32, 38), which can involve longer lead times for US buyers sourcing abroad. Perfume and treatment pumps frequently use the FEA standard (FEA 15, 18, 20), and glass droppers commonly use a GL18 / DIN18 finish. Airless systems often rely on dedicated, proprietary interfaces — which is one reason our airless jar guide notes that airless neck matches should be confirmed against the dispenser maker's drawing rather than assumed.

Sourcing Tips for Buyers

A few habits keep neck-finish problems off your production line:

• Request the neck drawing, not just the code. Confirm the minimum I dimension if filling speed, viscosity, plug fit or dip-tube clearance matters.
• Order a sample closure and bottle together and run a torque and leak test before bulk tooling.
• Use standardization to your advantage. A shared GPI/SPI finish lets you qualify backup suppliers without re-tooling — a point we expand on in the supplier vetting checklist.
• Match the finish to the product. Serums and oils favor 18/400–20/410 (serum bottles); lotions and body care run on 24/410; larger formats use 28/410; Boston rounds span 18/400–38/400; and lotion pumps and fine-mist sprayers are almost universally 410.
• Consider child-resistant needs early. CRC closures are built around specific finishes such as 20/400 and 28/410 — see the child-resistant packaging guide.

Vesspak supplies stock cosmetic bottles, jars and closures in standardized finishes with a low minimum order of 100 pieces, so you can prototype a matched bottle-and-closure assembly before scaling. We are a trade and wholesale supplier and do not sell food containers.

Frequently Asked Questions

Is a 24/410 cap the same as a 24/400 cap?

No. Both are 24 mm across the threads, but 400 has one thread turn and 410 has about one and a half. A 24/400 cap on a 24/410 bottle may thread partway and fail to seal — a frequent cause of leaks.

Does the first number tell me the opening size?

No. The first number is the outside thread diameter (T). The actual bore is the I dimension, which you should confirm on the drawing if your dip tube, nozzle or filling head needs clearance.

Are GPI and SPI finishes interchangeable with DIN?

Not automatically. DIN (European) and GPI/SPI (North American) use different pitch and engagement conventions. Confirm the closure maker's specification rather than assuming a match.

Standardization is what lets a small brand qualify multiple suppliers and keep dispensing consistent across a product line. When in doubt, send us your target closure or pump and we will confirm the compatible bottle finish from stock.