Tag Archives: metal caps

Metal Container Anatomy: Inside & Out

As the industry’s Metal Container leader since 1938 Freund Container has your answers for better packaging solutions.

WHY CHOOSE METAL? Metal is one of the most abundant raw materials, offering superior content protection and provides a very low environmental footprint.

Metal Liner Types:
C-Enamel liners work great for low acidic foods. For prolonged storing of foods with low acidity, however a discoloration of the metal surface can occur.
White Enamel liners are ideal for higher acidic foods, such as beets, berries, tomatoes, etc.
Epoxy liners are for most water and latex based solvents and increase chemical stability.
Laquer liners are FDA approved and work well for acidic food and aggressive solutions.

Frequently Asked Questions:
Heated Metal? Tinplate heat up to 450°F (230°C). Stainless Steel and Carbon can be heated to 2600°F.
Rusting Metal? Much of our metal is treated with a rust inhibitor, but not rust preventer. Rust is based on moisture and oxygen and however much exposure a container gets to either one of these post manufacturing is what will determine if any, how much rust you will incur. Testing is recommended with your product.


anatomy of a can 










Bead: concave (interior bead dot) or convex (exterior bead dot) area usually 1/8″ wide spanning the circumference of the tin to provide additional strength and stability to the tin bodyBody: a can without a cover (lid); the base of a containerCover: a can’s lid or closureCurl: area of tin turned in on itself to provide a safe, finished curved edge dotDome: a type of cover characterized by a flat horizontal surface (top) that tapers smoothly onto the skirt (vertical surface) dot

Drawn: see seamless

End: the area of a tin also known as the bottom. Coffee-style hermetic tins generally have two ends. Ends can be attached by seaming them on or crimping dot

Full friction: a plug-style metal cap fits snugly to the interior of the can dot

Hem: similar to a curl, an area of tin turned in on itself to provide a safe, finished flattened edge

Interior Friction: Cover/closure option in which a pliable ring fits to the interior of a tin allowing for a straight-sided slender profile can

Lock-seam: side walls meet and attach by hooking onto one another to form a tin body dot

Multiple friction: a plug closure fits into a “well” of a seamed-on ring. The plug is pressed into the ring and the two surfaces (the outside and inside edge) come into contact with the ring, creating multiple sealing surfaces on the plug/ring combination dot

Seamless: a tin that is constructed from a single piece of tin drawn to form the body of the can

Single friction: a plug-style metal cap fits snugly into a seamed on ring. The outside edge of the plug presses against the interior edge of the ring, creating one sealing surface dot

Slip cover: cover/closure style in which the cover’s skirt (vertical surface) slips over and to the outside of the can body dot dot

Stepped cover: type of slip cover in which a “step” is created between the horizontal surface and vertical surface of the cover so that stacking tins is possible with less likelihood of toppling over dot

Welded Seam: seam type in which side walls attach to one another through the use of heat to form a tin body dot

White Coat: entire surface of the metal is coated with white before applying other printing ink colors



Primary Container Closures: Don’t Get Them TWISTED!

Caps & ClosuresA dizzying array of container closures can be found in the rigid packaging market. Understanding the different types of closures will help you select the correct one. Each closure type performs a unique function. Here, we’ll focus on the two most common closure styles: continuous thread and lug style closures.

Continuous Thread Closures:Continuous Thread Closures

Continuous thread closures (also known as CT Finish Caps) are easily recognized by an unbroken, raised, spiral track on the inside of the cap. When mated to a container, the two spiral edges interlock in roughly 1 ½ turns, resulting in a tight, secure seal.

CT closures are available in both plastic and metal and successfully secure most contents, even when containers are tipped momentarily. Threaded closures, however, are not by default “LEAK-PROOF”. A definition of “LEAK-PROOF” systems is provided below.

Clearly, CT closures are utilitarian workhorses! They’re available with either a ribbed or smooth outer finish. Vertical ribbing on the outer finish provides superior gripping power for twisting closures – a useful feature when users’ hands are wet or slippery. CT closures are ideal for nearly any end-use application including chemical, health and beauty, automotive aftermarket, food and beverage, and medical products.

Lug Finish or “Quick” Twist Closures:

Lug Finish or Quick Twist Closures may be found on metal closures. Unlike their close relatives above, the spiral thread is intentionally broken to provide quick opening and closing. You’re likely thinking this compromises the closures sealing ability – that’s not entirely true. Rather than compromising its performance, this unique broken thread allows lug caps to seal in a quarter turn. Quick and easy opening and closing in a snap. Caps with this finish style are commonly used in canning products like jams and sauces, as well as beverage containers such as ice tea, juices, and other drinks.

Leak-Proof Container Systems:

You’re likely thinking, “Systems? I thought this was an article about closures.” Yes, leak-proof containers are sold as systems. Leak-proof container systems feature unique, interlocking threads on both the cap and container. Apply the closure to the container using the correct torque (twisting force) and the result is a leak-proof system – guaranteed. Two companies dominate this space: Nalgene and Kautex. Freund Container & Supply sells both and is proud to be North America’s exclusive Kautex supplier. Their unique design and relatively low sales volume drive their cost up. Cost aside, they deliver leak-free performance time and time again.

Now that we’ve covered basic closure styles, you should visit our Cap Sizer & Liner Definitions to learn about liner types, cap sizing, forming a seat seal, and about dispensing cap options or shop for Caps, Closures, and Liners now.