Will the cap fit? How to find your perfect lid.

One of the most important aspects of plastic packaging is ensuring you get the correct lid for your bottle. With the wrong sized cap, you won’t be able to secure your bottles, causing leaks and uneven surfaces. The key is to measure the thread count on your bottles and screw the cap down to meet the neck fully.

In this blog, we’ll outline what thread count is and how to find a cap that fits your plastic packaging bottle perfectly.

How do plastic bottles seal?

You may think that the cap is responsible for sealing a plastic bottle, but this is only partly true. 

Sealing a plastic bottle relies upon both the cap and the opening of the bottle making solid contact. Many caps have an inner material that assists this process for more challenging liquids and other caps have ‘lips’ that help make contact.

For most bottles, the thread size is the most important factor to consider when screwing down a cap, guaranteeing contact, and ensuring a tight seal.

What is thread size?

You may have noticed that many of our bottles have numbers following their names, like the Boston Round 415, 20mm. The first two words ‘Boston Round’ typically refers to the general shape of the bottle, while the numbers, 20mm and 415 in this case, refer to the bore and thread size.

The thread is the top part of the bottle where the cap screws on. 20mm is the diameter of this bottle, measured from the outer ends of the thread. 415 is known as the thread count, which is how many times the lid tuns before it is fully secured to the bottle.

The most common thread types are as follows:

  • 1 thread turn = 400
  • 1.5 thread turn = 410
  • 2 thread turns (tall) = 415
  • 2 thread turns (narrow) = 425

At B&I Polycontainers, our generic bottles range from 400 to 415, using the BSP (British Standard Pipe) thread type. Our bottles also use 5mm snap-on caps and 38mm ratchet caps for specific applications.


How to select the perfect fit

Finding the right fit for your bottle will depend on its intended use. Sometimes, you will need to store strong and dangerous chemicals. For this application, you may need a 38mm Ratchet cap, typically found on 1 litre bottles.

For typical packaging needs, your cap should be secure but easily removed. 5mm snap-on caps are ideal for this, typically found throughout the pharmaceutical industry. 

However, the key is to match the bottle’s thread size to your cap measurements and ensure the cap twists all the way down to the neck of the bottle to create a seal.


Seal the deal

Different bottles have different requirements. The caps you choose should reflect the bottle’s purpose while taking care of its practical application. As long you keep the thread and bore size in mind, this shouldn’t pose a problem.

B&I Polycontainers is a Proudly South African plastic bottle manufacturer and has decades of experience in supplying the best plastic bottles locally and internationally. We help you find the best plastic bottle for your packaging needs and support you with the production of high-quality plastic bottles and containers.

If you’re looking for packaging that won’t let you down, contact us today for free samples and a demonstration of our capabilities.


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