It is critical to find the right cap and neck finish for your packaging container. Every bottled product has a cap, container closure or stopper that needs a finish. We are here to guide you through common container cap and neck finish options. Let us look at the standard neck measurements as well as the common GPI/SPI neck finish and ways to measure it.
Identifying Closure Sizes
Continuous thread closure sizes or screw thread caps are always expressed with two numbers that are separated by a slash. The first number is the diameter (in millimeters) measured outside of the bottle’s thread or inside the cap’s opening. The second number is the thread style. Since the closure industry doesn’t always adhere to the same standards, it is always recommended that you purchase the caps and containers from the same manufacturer if possible.
Standard Neck Measurements
- T Dimension – This is the outer diameter of the thread. The T dimension’s tolerance range will determine the mate between the closure and the bottle.
- E Dimension – This is the outside diameter of the neck. The thread depth is determined by the difference between the T and E dimensions, divided by two.
- I Dimension – This is the inner diameter of the neck of the bottle. To allow sufficient clearance for filling tubes, specifications require a minimum I.
- S Dimension – This is measured from the top edge of the first thread to the top of the finish. The S dimension is the main factor in determining the amount of thread engagement between the cap and the bottle and the orientation of the closure to the bottle.
- H Dimension – This is the height of the neck finish. It is measured from the point of the neck where the diameter T intersects the shoulder.
Measuring the Neck Finish
It is easy to find the bottle neck finish. You will start by measuring from one side of the inner wall to the other. Next, measure the diameter of the outermost threads to calculate the neck finish. You will be able to find the T dimension, which will be the resulting millimeter measurement.
To determine the finish, you will have to see how many times the threads pass one another.
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