Why is it important to understand the type and dimensions of your bottle or jar neck and screw thread?
To get a compatible pack, for example a bottle and pump, or a jar and lid, you need to have - and understand - the accurate measurements and specifications of both your container and your closure. Understanding the difference between a 20/410 bottle and a 20/415 pipette, for example, will help you to select containers and closures that screw on well, avoid leakage, and function as they should.
- Neck Dimensions
- Standardised Neck Types
- Matching Closure to Container
- Additional Features
- Bringing it all Together
Let's start by looking at the important dimensions which are often talked about, when looking at the neck of a bottle. Understanding these gives you a good background to understanding the fit between the closure and bottle - although there are some standardised neck fittings to make it easier to ensure compatibility, and we'll come onto those later.
For now, here are letters used to refer to various neck dimensions on a bottle or jar:
T Dimension: The measurement from the outside edge of the thread on one side of the neck, to the outside edge of the thread on the opposite side.
E Dimension: The outside diameter of the neck (without including the thread). We always remember this one by thinking E = 'External'. Any inserts, such as a shive or a dropper insert, must have a head that is slightly smaller than the E dimension, otherwise they risk fouling on the closure as it is screwed on.
I Dimension: The inner diameter of the neck. We remember this one by I = 'Internal'. An important measurement to know when machine filling a bottle - usually it must be large enough to allow a filling tube to pass through it.
S Dimension: The distance from the top of the 'finish' (the flat surface on the very top) down to the top edge of the thread at its highest point.
H Dimension: Measured from the top of the finish, down to the shoulder. To tell exactly where this should be measured to, you take the diameter of the T dimension, and carry it straight down to the point where it intersects the shoulder.
Standardised neck types
So as we said, the above dimensions are very important to understand. However in the first instance, you can get a very clear idea of compatibility just by using some of the many standadised neck thread types out there. These standardised terms are used to describe both necks and closures. We'll review a few of these below:
DIN 18 (or 18DIN): this is an 18mm diameter (T dimension) standardised finish widely used in Europe. It originated in Germany, with DIN being an acronym for Deutsches Institut für Normung, the German standards institute. Usually seen on dropper bottles, this means that the bottle neck has a standard height and diameter - and also that it always has a 'bead' (protruding ring) at the bottom of the neck, to ensure compatibility with tamper-evident closures. The bead ensures that the break-off band on such closures functions correctly when unscrewed for the first time.
GL18: This is very similar to DIN 18, but is the French version. Most aspects of this are pretty much identical to the DIN 18. One difference is that GL18 does not necessarily mean that the neck includes a tamper evident bead - although GL18 bottles can, and often do, still have the bead. There are also GL20 (20mm diameter) and GL22 (22mm diameter) versions of this thread type.
20/400 (or 20-400): Neck types written in this format are norms which originated from the Glass Packaging Institute (GPI) in the USA. in this instance, the '20' part refers to the 20mm T dimension (thread diameter), and the '400' refers to the thread type - it has one complete turn around the bottle (see diagram).
20/410 (or 20-410): As above, another GPI standard. 20mm diameter, and the '410' means one and a half turns of the thread around the neck (see diagram). Let's throw in another piece of information here in case you're getting confused with initials you've seen somewhere else: the Glass Packaging Institute (GPI) was formerly known as the Glass Containers Manufacturer's Institute (GCMI) - so if you've found either of these initialisms anywhere, they refer to the same thing!
20/415 (or 20-415): As above, a 20mm diameter, with '415' meaning two complete turns of the thread around the neck (see diagram).
22/400, 22/410, 22/415 (22-400, 22-410, 22-415): Alright. We know you've already got this. The 22 is the T dimension, and the other part denotes which type of thread it is, as per the diagram.
24/400, 24/410, 24/415 (24-400, 24-410, 24-415): Did you know that 24mm diameter is another common standard of GPI thread, just like the others listed above? Yes, thought so.
28/400, 28/410, 28/415 (28-400, 28-410, 28-415): Isn't this fun? Did you know that 28mm diameter is another common standard of GPI thread... (Sorry. We'll stop now.)
Oh no, wait. What is an R3/20 closure? Or an R3/22 bottle neck? Or an R3/24? Or an R3/28? This is exactly the same as the '400' type thread used by the GPI. So, 20/400 = R3/20, for example. Actually, on our site, you will always find the 'R3' term used rather than the '400', just to save a little confusion.
PP28 (or ROPP28): another 28mm diameter closure type - it doesn't quite match to any of the GPI threadforms. ROPP stands for Roll-On Pilfer Proof, and the history behind this is from glass bottles where a plain metal cap was placed over the top of the bottle, covering the thread, then its sides literally rolled using a machine, so that the metal conformed to the bottle thread exactly - providing a secure closure and great seal. Closure manufacturers eventually copied the thread pattern used on the bottles and produced it as a standard pre-moulded closure, for additional convenience.
And our closing note... you can tell we love this subject... you'll notice some of the terms above refer to glass bottles. This is simply because glass is one of the oldest commonly-used packaging materials in existence, so there were existing standards for them when plastic bottles were introduced. To avoid adding confusion, plastic bottles used the same terms, helping to achieve more versatility between products.
Matching closure to container
So now you know how to match a container to a closure - you just select a bottle and a lid that have the same number against them! ...or do you?
Yes, you knew there'd be a catch.
Actually, in theory it really is that simple. In practice however, there are many more variables to keep in mind. Variations and tolerances, while still standardised, really mean that you should consider taking a good selection of samples of any container/closure combination, to thoroughly test their compatibility. In addition, ingredients within your formulation can react to some materials, to the extent that they can cause a perfectly compatible container and closure to fail or leak. Just to be clear, that even includes 100% natural ingredients (think essential oils in contact with certain plastics, for example).
you should consider taking a good selection of samples of any container/closure combination, to thoroughly test their compatibility
Established brands always have a rigorous testing programme, and we know we don't need to tell most of you this, but whatever size your brand is, it's worth taking a leaf out of their book. You'll often hear of people talking about a '12-week compat test' - and there's a really good reason for extended tests like this (and longer ones too), because they come as close as possible to simulating the real-life journey of the product from the filling line, through storage and/or retail, and all the way to the consumer's shelf (or - and this raises the bar quite a bit - the consumer's expensive handbag, where it may spend an extended time on its side or upside-down, alongside other expensive contents in there)! Yes, it really is worth doing your homework.
Other tests you may want to consider include leak tests, vacuum chamber tests, and drop tests - all things which help to imitate the rigours that a product will go through once it leaves the filling line. And speaking of filling lines - have you double-checked with your production-line manager (or your contract filler) whether the pack will easily pass through their filling lines? An easy one to miss, definitely worth sparing a thought for to avoid any embarrassing initial problems!
In this industry, we love acronyms - when you first step out in it, you often feel like you're learning the alphabet all over again!
Here are some more terms you might see, relating to additional features found in some of our closures:
CRC (Child Resistant Closure): The ISO 8317:2015 standard defines child-resistant packaging as 'packaging that is difficult for a child younger than 52 months to open, but not difficult for an adult to use properly'. In more common terms, 52 months is 4-and-a-bit years old, just to help put it in perspective. CRC refers to closures with features like 'push down and turn to open' or with side flanges which must be pressed while turning to open.
TE (Tamper Evident): Closures that have visual proof that the pack has been tampered with or opened, such as a break-off ring - which works by pushing the perforated ring at the bottom of the closure over the bead on the bottle neck on the assembly line (and in some cases rolling the ring in firmly under the bead). When the cap is unscrewed, the additional pressure of the bead is enough to snap off the perforated part.
CRC/TE (Child Resistant and Tamper Evident): More and more, closures now have both of the above features in them - they are both resistant to young children AND they show when they have been opened. Have a look at these pipettes or these dropper caps for some examples of closures demonstrating both features.
IHS (Induction Heat Seal): A closure which incorporates a foil liner below the wad. When screwed on, the pack then passes under an induction heat source, which firmly seals the foil onto the bottle finish. When the cap is removed by the consumer, the foil is left adhered onto the bottle, ensuring the pack contents remain sealed right up until first use.
Bringing it all together...
By now we're hoping you've found that piece of information you were looking for. Or that you might have even found bits of this quite interesting. And we're wondering if actually, given that we know one or two people who assumed that choosing packaging was a last-minute simple job, you're realising why the whole thing can suddenly become such a tricky topic!
If the latter is true of you - stay right with it. Getting the right packaging can actually enhance your customers' experience. While it might be a tad suprising to spend months and months on your unique skincare formulation, only to get 5-star reviews praising only how light the spray feels when it touches your face (because of the special atomiser you chose) - you'll definitely want to have it that way round, rather than the packaging letting the side down after all those months of painstaking chemistry!
And don't worry, you're not alone. Reach out to us, give us a call on 01355 236 170, or even hit the chat box at the bottom right. If it says 'online' that means there's a real person sitting right at the other end, waiting to help on your enquiry. Our experts love talking through all this stuff, and they have the advantage of doing it every day (and have done for years and years). We're looking forward to the chat already!