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Continuous-thread Closures

C-T closures involve actual twists and turns on the part of the consumer, but brand owners face figurative twists and turns in delivering a positive use experience.

Sterling Anthony
Sterling Anthony

Continuous thread (C-T) closures are meant to be applied to containers (e.g., bottles, jugs, jars, tubes, aseptic cartons) that have matching C-T finishes (necks). The matching needs to be in terms of dimensions and styles, for the container and closure to combine in a secure fit. The designation, C-T, means that the thread travels a continuous spiral around the finish, unlike with a lug finish, wherein, the thread is interrupted and not continuous. C-T closures are used in a wide variety of product categories, including food, beverage, cosmetics, personal-care, pharmaceuticals, and household chemicals, among others.

The wide use of C-T closures bespeaks its simplicity. The conveniences of easy opening and easy reclosing are accomplished with a counterclockwise turn and a clockwise turn, respectively. That simplicity, though, is an end-result that’s in contrast to the complexities that preceded it. Packaging suppliers, packaging designers, and packaging users (i.e., brand owners) had to have managed a host of factors and considerations. Convenience is not the only function affected—in addition, there are containment, protection, and communication. As if that wasn’t enough, aesthetics also can come into play.

As with all packaging-related undertakings, decisions start with the product. It stands to reason that products with dissimilar characteristics will have dissimilar needs regarding C-T closures. Reflecting this fact, C-T closures are available in standard stock designs, as well as specialized designs to accommodate requirements such as trigger spraying, dispensing, measuring/dosing, tamper-evidence (T-E), and child-resistance (C-R).

Specifying C-T closures and containers that have C-T finishes is facilitated by standardized nomenclature, such as that of the Glass Packaging Institute and the Plastics Industry Association (PLASTICS). Dimensions are designated by letters. For a container’s finish, T is the outside diameter across the threads, E is the outside diameter within the threads, I is the inside diameter, S is the measurement from the top of the finish to the top of the first thread, and H is the height (the measurement from the top of the finish to the bottom of the finish, where it meets the container’s shoulder). For a C-T closure, the same letters are used in a mirroring fashion, given that the closure overlays the finish and that the external threads of the finish glide up and down the internal thread tracks of the closure.

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