What You Need to Know About Cap and Neck Finishes

What You Need to Know About Cap and Neck Finishes

Neck finishes are an important part of bottling. Neck finishes and caps prevent the contents of the container from spilling as well as prevent foreign objects from entering the container. Neck finishes can also add an aesthetic quality to the product that customers are sure to appreciate.

What is a neck finish?

Plastic bottles, glass bottles and other containers’ neck have a finish that holds the cap. The neck finish refers to the top section following the opening of a bottle, jar, or any other container with protruding threads that wrap around the outside of the container to securely fasten a matching cap.

A cap is a common type of closure for bottles, jars, and tubes that seals the contents of the container. The container and its corresponding cap must have a matching finish. For example, a 24/400 bottle will only accept a 24/400 bottle cap, so as to prevent any contents in the container from escaping, as well as prevent foreign substances from entering the container. It makes sense that the terms that are used to designate the size of a cap are the same terms that are used to indicate the neck finish of a bottle.

If you have an existing bottle or cap in your inventory and want to find a matching cap or bottle, it is important that you clearly understand the cap size or neck finish dimensions.

Before purchasing caps, lotion pump, trigger sprayer, plastic bottle or glass bottles, you will be asked about the size of the cap or dimension of the neck finish. Common neck finish dimensions are 24/400, 24/410, and 28/410.

It is obviously very important to know the accurate size for each product order you make. So how do you accurately determine the cap size or the neck finish of a bottle and make the right purchase?

How to accurately determine the cap size or the neck finish of a bottle

The first step is to understand how cap sizes and neck finishes are measured. Knowing this will help you make better decisions about which cap type and size you really need and prevents error-prone guesswork.

How cap sizes and neck finishes are defined

The length and number of threads are specifically designed to securely seal different types of products. The threads also determine how the container will be sealed. The most common types of thread are the continuous threads which require a twisting motion to unlock. Other caps such as lugs only require a single motion to unlock.

Let’s dive into a little bit of detail on both types of threads.

1.     The Continuous Thread – abbreviated “CT”.

Cap sizes and neck finishes are expressed as two numbers separated by a dash (24-400), a fraction (24/400) or as a single number (24mm).

The first number refers to the diameter of the cap or bottle opening (in millimeters) and refers to the nominal diameter measured across the inside of the cap at the opening or the outer diameter of the bottle. For caps, this number represents the inner diameter of the cap. For the neck finish, this number represents the outside diameter of the threads on the neck of the bottle.

The second number refers to the thread style, “GPI” or “SPI” finish. This refers to the height of the cap and the style of threads on the cap and the container.

The Glass Packaging Institute (GPI) and Society of the Plastics Industry (SPI) are responsible for establishing uniform standards for glass and plastic container neck finishes. The critera that makes up these standards incorporates thread turns, distance between threads, height, top beads, and continuous vs non-continuous threads.

2.     Lugs –also known as the “Twist Off” finish (abbreviated “T/O”)

Lug finishes are only found on glass containers. Lug finishes can be identified as the diameter (e.g. 38mm) followed by T/O (abbreviated for Twist-Off). This example refers to 38mm T/O.

Standard Neck Measurements

  • “T” Dimension – The outside diameter of the thread. The tolerance range of the “T” dimension will determine the mate between bottle and closure.
  • “E” Dimension – The outside diameter of the neck. The difference between the “E” and “T” dimensions divided by two (E-T/2) determines the thread depth.
  • “I” Dimension – The inner diameter of the bottle neck. Specifications require a minimum “I” to allow sufficient clearance for filling tubes. Linerless closures, with a plug or land seal, and dispensing plugs and fitments require a controlled “I” dimension for a proper fit.
  • “S” Dimension – Measured from the top of the finish to the top edge of the first thread. The “S” dimension is the key factor that 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.

Engineers define many technical dimensions when designing the bottle, such as T, E, I, S, H, etc. However, you only need to pay attention to two numbers: neck diameter and neck finish (or thread design).

Common GPI/SPI Neck Finishes

The most common thread styles are shown in the image below. Each style is designated by a number. The differences among threads styles are the number of thread turns and height of the neck finish.

  • 400: 1 thread turn
  • 410: 1.5 thread turns
  • 415: 2 thread turns, Tall neck finish
  • 425: 2 thread turns, Narrow Threads
  • 430: Buttress Finish – thick threads and top bead (better seal, more application torque)
  • 2000: Lug Finish – Non-continuous threads(Commonly used with glass containers in the food industry)

There are also some special neck finishes worth mentioning, such as the:

·       DBJ (continuous thread)

A DBJ neck finish features a ring beneath the threads that catches on to a detachable ring of a DBJ cap. When the end user unscrews the cap from the container for the first time, the ring will break off from the cap, making it tamper evident.

·       470 (continuous thread)

A 470-neck finish consists of one thread turn and is commonly found on glass Mayo jars. The threads of a 470-neck finish are deeper than a 400 finish.

How to Measure a Neck Finish

Measuring a bottle neck finish dimensions is a simple process. Here’s a list of simple steps you can follow to measure neck finishes.

  1. Start by measuring from one side of the inner wall to the opposite side.
  2. Calculate the neck finish by measuring the diameter of the outermost threads. The resulting millimeter measurement will be the “T” dimension.
  3. Count how many times the threads pass one another to determine the finish. For example, a 28 mm “T” dimension with 1.5 thread turns equals a 28/410 neck finish.

As you can see from the picture, the dashed red line indicates the inside diameter of the cap as well as the outside diameter of the threads on the neck of the bottle. In this example, the number for both is 28.

The threads make one and a half thread turns around the bottle. Comparing this with the common thread styles image indicates that the thread style is a 410. The diameter is 28mm and the thread style is a 410, so the cap size and neck finish for our example is 28/410.

Easy isn’t it?

Congratulations! You now know what a neck finish is and how to accurately measure cap sizes and the dimensions of neck finishes. This is a useful skill to have if you make purchasing decisions or if you need large quantities of product packaging. If you have any questions, feel free to reach out to us.

One of the best things we do at Packbien is to provide customized and quality caps, pumps and bottles in various sizes and colors. With a long history of satisfied customers, we’re proud to say we deliver only the best packing solutions. Click the link below to go to browse our list of packing solutions. https://packbien.com/

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