If you've ever tried to replace a bottle cap or design packaging for your product, you've probably realized that figuring out the bottle neck size isn't as simple as grabbing a ruler and guessing. The neck finish (or opening size) determines what kind of cap, closure, or dispenser will fit your bottle properly. Get it wrong, and you'll either end up with a loose cap that leaks or one that simply won't screw on at all.
Understanding Bottleneck Size
In the packaging industry, bottle neck size is measured using a two-part system - for example, 38-400 or 28-410. The first number (before the dash) represents the diameter of the bottle's neck opening in millimeters, while the second number (after the dash) refers to the thread style or finish, which determines the type of cap that fits.
So if you see "38-400," that means:
The neck has a 38 mm outer diameter.
The "400" indicates a standard continuous thread design, with a specific thread height and pitch commonly used for screw-on caps.
Each neck finish standard - 400, 410, 415, 425, etc. - follows the GPI (Glass Packaging Institute) specifications, which packaging manufacturers use worldwide to ensure compatibility between bottles and caps.
How to Measure Bottle Neck Size Yourself
If you don't have the official spec sheet, you can still measure it manually using a few simple tools:
Measure the outer diameter of the neck opening (in millimeters) with a caliper. This gives you the first part of the neck size.
Count the number of threads (or turns) along the neck. Most common plastic bottles have continuous threads - you can visually check if the threads are wide or fine.
Estimate the thread pitch and height - this can be tricky, so many people compare their bottle to an existing reference chart or an old cap that fits.
If your cap doesn't match perfectly, it's usually because the thread finish (the "400" part) is different, even if the diameter is the same.
Common Neck Sizes
Here are a few of the most commonly used neck finishes in the plastic bottle industry:
28-400 / 28-410: Often used for food, cosmetic, or supplement bottles.
38-400: Common for juice bottles, protein powder containers, and wide-mouth jars.
45-400 or 53-400: Used for larger bottles and jars, especially in food packaging.
63-400 or 90-400: Found on bulk containers and wide-mouth PET jars.
These standards make it easier for manufacturers and brands to source compatible caps from multiple suppliers.
Why Neck Size Matters
Choosing the right neck size isn't only about fitting the cap - it also affects sealing performance, leak resistance, and user experience. A slightly off-thread or mismatched cap can lead to leakage, contamination, or product spoilage, especially for liquids or sensitive foods. For companies, that means wasted product and unhappy customers.
That's why professional bottle manufacturers use precision molds and strict quality testing to maintain consistent neck dimensions across every batch.
Final Thoughts
Whether you're creating your first product line or replacing caps for existing bottles, understanding bottle neck sizes can save you time, money, and frustration. When in doubt, always check the technical drawing or request a neck finish sample before bulk purchasing closures.
At Hubei Mingda Plastics Products Co., Ltd., we manufacture a full range of PET and HDPE bottles with standard neck finishes like 38-400, 45-400, 53-400, and more - all tested for sealing performance and thread accuracy.
If you'd like to learn more or need samples for your project, [contact us here →]