The Neck Finishes on Plastics Manufacturing of a plastic bottle holds the closure onto the container with protruding threads. When determining the compatibility of continuous thread (CT) closures, it is important that both the bottle neck and closure have the same finish.

The finish of a CT bottle is composed of two numbers separated by a hyphen, such as 28-400. The first number is the outside thread diameter of the container in millimeters. The second number is the thread style or finish. That number determines the number of turns required to seat the closure on the container.

Uniform standards for neck finishes for plastic bottles have been set by The Society of the Plastics Industry (SPI). The closure industry doesn’t always adhere to SPI standards so it is important that the bottle and closure are tested together prior to ordering.

To learn more about neck finishes click HERE.  To request samples click HERE.

“H” Dimension: The height of the neck finish. Measured from the top of the neck to the point where the diameter, “T”, extends down and intersects the shoulder.

“S” Dimension: Measured from the top of the finish to the top edge of the first thread. The “S” dimension is the key factor in determining the orientation of the closure to the bottle and the amount of thread engagement between the bottle and cap.

“I” Dimension: The inner diameter of the bottle neck. Specifications require a minimum “I” to allow sufficient clearance for filling tubes. Linerless closures, with a plug or land seal, and dispensing plugs and fitments require a controlled “I” for a proper fit.

“T” Dimension: The outside diameter of the thread. The tolerance of the “T” dimension determines the mate between bottle and closure.

“E” Dimension: The minor diameter measured across the root of the threads.