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A neck finish code like “24-410” is the handshake between a bottle and its cap. Get it right and closures seat and seal first time. Get it wrong and caps back off, cross-thread or leak in transit. The code looks cryptic, but it’s just two numbers.
What the two numbers mean
The first number is the outside diameter of the neck in millimetres — 24 means a 24 mm neck. The second is a GPI/SPI code describing the thread style and finish height: 400 is a rolled single-turn thread, 410 is a taller single turn, and 415 is taller still for a more secure seal.
Why the second number matters
Two necks can share the same 24 mm diameter but differ in thread pitch and height. A 24-410 cap will not tighten correctly onto a 24-415 neck. The diameter tells you the cap size; the finish code tells you whether it will actually thread on.
Common finishes you’ll meet
- 400 — one turn, rolled finish; economical, general purpose.
- 410 — one turn but taller; a more secure engagement.
- 415 — taller again; favored where a tight seal matters.
- Continuous thread (CT) vs. snap-on, dropper and pump necks each pair with their own closures.
Before you order
- Match the neck code to the closure supplier’s spec, not just the diameter.
- Confirm the liner or sealing type for your product (oil, alcohol, food).
- For droppers and pumps, confirm the dip-tube length to the bottle base.
- Ask for a neck-finish drawing so nothing is assumed.
Specify the neck finish and the closure together — glass and cap are one system, never two separate line items.
Not sure of your code? Send the bottle, or a caliper reading of the neck outside diameter, and we’ll identify the finish and the closures that fit it.
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