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SKS Bottle & Packaging 29th Anniversary


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Cap and Neck Finishes Cap and Neck Finishes

A container's neck finish holds the cap, stopper, or closure with protruding threads. A container and its corresponding cap must have matching finishes. For example, a 24/400 bottle will only accept a 24/400 closure.

Screw thread or continuous thread closure sizes are expressed with two numbers separated by a hyphen or slash. The first number refers to the millimeter diameter measured across the inside of the cap's opening or the outside of the bottle's threads. The second number refers to the thread style, "GPI" or "SPI" finish. The Glass Packaging Institute (GPI) and Society of the Plastics Industry (SPI) are responsible for establishing uniform standards for glass and plastic container neck finishes. The closure industry does not necessarily adhere to the same standards, so it is often best practice to purchase containers and caps from the same manufacturer when possible.

For information about proper torque when applying closures to containers, visit our Torque Guide page





Common GPI / SPI Neck Finishes

Standard Neck Finishes
  • 400
    1 thread turn
  • 410
    1.5 thread
    turns
  • 415
    2 thread turns,
    tall "H" dimension
  • 425
    2 thread turns,
    narrow
    threads
  • 430
    Buttress finish:
    thick threads
    & top bead
    (better seal, more application torque)
  • 2030
    Lug finish:
    Non-continuous
    threads
  • 2035
    Lug finish:
    Non-continuous
    threads, tall "H" dimension





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 outermost threads. The resulting millimeter measurement will be the "T" dimension.

How to Measure a Neck Finish


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)



Thursday 27 August, 2015