How to Measure the Neck Finish of your Bottle or Cap

Neck Finishes

The neck finish is the opening at the top of a container or bottle where you twist down the cap, or closure. Thereby creating a tight seal. This is done via a series of protruding molded-in “threads” that spiral down around the outside of the neck. It’s essential that you choose a cap or closure that matches the neck measurement of your container. For example, a 38/400 cap will only fit onto a 38/400 bottle neck.

The length and number of threads determine how a cap seals to a container. The most common thread styles use what are called "continuous" threads which spiral around the containers neck. These threads have matching threads molded into the inside diameter of the cap. Continuous thread systems require the cap being twisted into place.

Neck Finishes are identified with a system that uses two numbers separated by a slash or a dash. The first number is the diameter (in millimeters) of the inside of the cap’s opening, or the outside of the bottle’s threads. The second number is the style of the thread. We advise that you procure samples of the bottle and cap you intend to use to make sure they match. Especially if you choose them from separate suppliers.

Standard Neck Finishes - “The following are a list of industry standardized measurements for determining and identifying bottle neck finishes.

"T" Dimension - The outside diameter of the thread.

"E" Dimension - The outside diameter of the container’s neck. The difference between the “E” and “T” dimensions divided by two determines the thread depth.

"I" Dimension - The inner diameter of the neck. Specifications require a minimum “I” to allow sufficient clearance for filling tubes, and for certain polycone lined caps, and dispensing caps.

"S" Dimension - Measured from the top of the finish to the top edge of the first thread. The “S” dimension determines the orientation of the closure to the bottle and the amount of thread engagement between the bottle and cap.

"H" Dimension - The height of the neck finish. Measured from the top of the neck to the point where the diameter “T”, extended down, intersects the shoulder.

Measuring a Neck Finish

1. Measure the DIAMETER of the INSIDE of the cap. (Measure from one side of the inner wall to the opposite side.) Or, measure the bottle’s neck finish by measuring the OUTSIDE DIAMETER of the threads. This will give you the “T” dimension..

2. Count how many times the threads pass one another to determine the finish. For example, a 38 mm “T” dimension with 1 thread turn = 38/400 neck finish.

Is There a Simpler Way to Measure the Neck Finish of my Bottle?

Yes there is! For your convenience, we've created a helpful picture template for measuring the Neck Finish of your bottles. Simply print out the picture. Lay it down the on a flat surface. Then flip your bottle upside down and place it, neck down, onto the template. The circle that matches the diameter of your bottle is the Neck Finish.

Use this accurate, lifesize guide to find out the mm Neck Finish size of your bottle or jar. Simply set the mouth of your bottle or jar down over the circles below. The circle that fits, is the Neck Finish.

If you have any more questions, welcome to contact us.