How to Measure a Bottle's Neck Finish

1. Understand what the two numbers in a neck finish mean - A neck finish is written as two numbers, like 24-410 or 20-400. The first number is the outer diameter of the threaded neck in millimeters. The second, three-digit number identifies the thread style and design - it tells you the thread's shape and how many threads wrap around the neck, not the size. Both numbers have to match for a cap to actually fit, even if the diameter alone looks right.
2. Measure across the outer edge of the threads, not the very top of the bottle - The most common measuring mistake is measuring the bottle's outer rim or inside opening instead of the threads themselves. Using a caliper, measure straight across the widest point of the threaded ring near the top of the neck - the actual raised, spiraled ridge a cap screws onto, not the smooth lip above or below.
3. Round to the nearest standard size, not your raw measurement - Neck finishes come in a defined set of standard sizes - common ones include 18, 20, 22, 24, 28, 33, 38, 43, 45, and 48 mm, among others. A caliper reading of 23.6 mm almost certainly means a 24 mm finish manufactured within normal tolerance, not a nonstandard size - always round to the nearest real, published finish size.
4. Count the thread starts to help narrow down the finish series - Some finishes use a single continuous thread, while others use two parallel threads running side by side - look closely at where the thread begins at the top of the neck to see if there's one starting point or two. This detail, combined with the diameter, helps you tell apart finish codes that otherwise look very similar at a glance.

5. Cross-check against a sample cap before ordering in bulk - Because several neck finishes can look nearly identical, the most reliable confirmation is testing a real cap on your bottle before placing a large order. Free product samples are offered on the product pages for most SKS Bottle & Packaging items.
6. For SKS bottles and caps, check the Cap Code instead, and shop Add-Ons - When you're ordering your containers and closures from SKS, there's a faster and easier way! Every bottle, jar and cap on our site carries a simple list of cap codes, and any cap sharing that same code is a guaranteed fit. Look for the Compatible Add-Ons button beneath the stock number on any product page to see matching items and add them to your cart.

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Measuring a Bottle Neck Finish FAQ

Reading a bottle's neck finish correctly comes down to measuring the right part of the bottle and matching both numbers in the code, not just the diameter. If you're working with anything from our own catalog, checking the Cap Code is faster and more reliable than measuring by hand at all.

What Do the Two Numbers in a Neck Finish Mean?

The first number is the outer thread diameter in millimeters, and the second, three-digit number identifies the thread's specific style and design - both numbers must match for a cap to fit correctly.

Where Exactly Should I Measure on the Bottle Neck?

Measure across the widest point of the threaded ring itself, not the smooth rim above or below it - measuring the wrong part of the neck is the most common mistake people make.

What If My Measurement Falls Between Two Standard Sizes?

Neck finishes come in a defined set of standard sizes, so a measurement like 23.6 mm almost always means a 24 mm finish within normal manufacturing tolerance, not a true nonstandard size.

What Is a Cap Code, and How Is It Different From a Neck Finish?

A Cap Code is our own simple code assigned to bottles and caps in our catalog - any cap sharing the same code as a bottle is guaranteed to fit, making it a faster shortcut than measuring a neck finish by hand.

Is There a Reliable Way to Confirm a Finish Before Ordering in Bulk?

For anything outside our catalog, ordering one sample cap to physically test the fit is the safest way to confirm a match. For our own products, checking the Cap Code or Compatible Add-Ons button is the faster, more reliable option.

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