It is important when considering packaging to have a clear understanding of neck finish dimensions. When selecting a closure for a container there are several measurements needed to ensure a secure and sealed fit.
The packaging experts at C.L. Smith are available to provide assistance with any questions or additional resources needed for determining the neck finish dimensions of a container.
Neck Finish Dimensions
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” dimension for a proper fit
The outside diameter of the thread. The tolerance range of the “T” dimension will determine the mate between bottle and closure
The outside diameter of the neck. The difference between the “E” and “T” dimensions divided by two determines the thread depth.
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.
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.
Common GPI/SPI Neck Finishes
The official Glass Packaging Institute is a series of voluntary standards that allow for compatibility between manufacturers and users of containers & closures. The critera that makes up these standards incorporates thread turns, distance between threads, height, top beads, & continuous vs non-continuous threads.
How to Measure a Neck Finish
To find a cap’s diameter, measure from one side of the inner wall to the opposite side. Calculate a bottle’s neck finish by measuring the diameter of the outmost threads. The resulting millimeter measurement will be the “T” dimension.
Then, see how many times the threads pass one another to determine the finish.
(ex. 24 mm “T” dimension with 1.5 thread turns = 24/410 neck finish)