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:
Neck Finish Dimensions
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.
Last Edited: 5/28/2021
The information contained in this article is for general information purposes only. The information is provided by
United States Plastic Corp. and while we endeavor to keep the information up to date and correct, we make no representations or
warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with
respect to the website or the information, products, services, or related graphics contained on the website for any purpose.
Any reliance you place on such information is therefore strictly at your own risk.
In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss
or damage, or any loss or damage whatsoever arising from loss of materials, time or profits arising out of,
or in connection with, the use of this information.