Lug-type and continuous-thread closures

Lug-type and continuous-thread closures

If acronyms like CT, TW, T/O, or Lug look familiar, they’re shorthand used in the packaging industry to describe cap styles and the way they thread onto bottles and jars. The best choice can vary based on what’s inside the container and the sealing method, as each closure type can offer different advantages.

Caps typically come in two finish styles: Continuous Thread (CT) and Lug, also known as twist-off, TW, or T/O. With a CT neck finish, a single, unbroken thread spirals entirely around the container’s opening.

CT finishes are typically noted as “xx/400” or “xx/450.” For instance, a “70/450 Gold Metal Plastisol Lined Cap” means the closure has a 70 mm opening and matches a 450-series thread profile and depth. Any thread designation in the 400s identifies a continuous-thread (CT) cap.

When a CT cap is screwed onto a container, the cap’s internal ridge engages the container’s threads and tightens as you turn it. These closures are ideal for manual use because they can be fully tightened without risking damage or stripping of the threads.

A lug (twist-off) finish isn’t the same as a continuous thread. Instead of one unbroken spiral, the neck has interrupted segments that form several separate threads around the mouth. These finishes are typically designated as “xx mm T/O” or “xx-2020.” In these codes, the first number is the mouth diameter in millimeters, while the second indicates the thread style per GPI standards. When that second number falls in the 2000 series, it signifies a lug finish.

Compared with continuous-thread (CT) caps, lug caps aren’t as easy to put on manually. They’re intended for use with capping equipment, which can apply the precise torque needed to form a proper seal. When you do tighten them by hand, they usually need only about a quarter turn — far fewer turns than a CT cap. Over-tightening a lug cap can strip it, rendering it useless. On the plus side, lug closures are typically less expensive than CT caps.

Want the lowdown on continuous thread and lug finishes, or unsure which cap fits your bottle or jar line? Reach out by phone, send us an email, or start a LiveChat right here on our site. Our packaging specialists are standing by to assist!