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Cap and Neck Finishes

Screw thread cap sizes are generally expressed as two numbers. The first number refers to the cap diameter (in millimeters) and the corresponding Glass Packaging Institute (GPI)/Society of the Plastics Industry (SPI) finish diameter. The second number refers to the height and thread configuration of the closure or finish. The following is a selection of commonly used caps and finishes:
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Neck Finish Dimensions

"T" Dimension
"E" Dimension
"I" Dimension
"S" Dimension
"H" Dimension
To learn more about the dimension and how they are measured, click on the titles below to reveal definitions.

"T" Dimension

The "T" dimensions refers to the outside diameter of the thread. The tolerance range of the "T" dimension will determine the fit between the bottle and closure.

"E" Dimension

The outside diameter of the neck. The difference between the "E" and "T" dimensions, divided by two, 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. Liner-less 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 which 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.

Caps you may be interested in...

Title: How to measure and calculate cap & neck sizes
Description: A brief explanation on understanding the cap & neck finish on bottles.
Published: 7/21/2003
Last Edited: 5/28/2021
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