Understanding Neck Finish: The Key to Ensuring a Perfect Fit Between Bottles and Closures

What Is a Neck Finish?

The term “neck finish” refers to the international standard specification for bottle thread sizes, which determines how the bottle and its closure (such as a cap, pump, or sprayer) connect.

Common neck finishes include 18, 20, 24, 28, and 33, where the number represents the outer diameter of the thread in millimeters (mm).

For example, a “24” neck finish means the thread’s outer diameter is 24 mm.

Neck Finish and Capacity Are Not Directly Related

Bottle capacity and neck finish size do not necessarily correspond. For instance:

• LV177 – 500ml square bottle: 33 neck finish
• LV06 – 500ml handle bottle: 28 neck finish

This shows that even bottles with the same capacity can have different neck finishes.

Why Must the Neck Finish Match?

The bottle and its closure (such as a pump or trigger sprayer) must have the same neck finish to fit properly. For example:

• A 28-neck bottle with a 33-neck pump will not fit because the pump cap is too large to tighten.
• Conversely, a 33-neck bottle with a 28-neck sprayer will not work because the sprayer cap is too small.

In short, matching neck finishes is the first and most crucial step to ensure a proper fit between bottles and closures.

Proper Fit Isn't Enough — Testing Is Essential

Even when the neck finish matches, additional testing is required before confirming product usability. These include:

• Leakage tests: To ensure the product does not leak.
• Compatibility tests: To verify that the contents do not react chemically with the bottle or closure materials.

Only after passing these tests can the product be considered truly viable for production and procurement.

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