General Cap & Liner Info

Cap and Neck Finishes

“T” Dimension – The outside diameter of the thread. The tolerance range of the “T” dimension will determine the mate between bottle and closure.

“E” Dimension – The outside diameter of the neck. The difference between the “E” and “T” dimensions divided by two determines the thread depth.

“I” Dimension – 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.

“S” Dimension – 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.
Cap top

“H” Dimension – 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.


Different Sizes of Cap Top

Screw thread cap sizes are generally expressed as two numbers. The first number refers to the cap diameter (in millimeters) and the corresponding Glass Packaging Institute (GPI)/Society of the Plastics Industry (SPI) finish diameter.

The second number refers to the height and thread configuration of the closure or finish.

Selecting a Cap Liner Type

Selecting the type of liner for your cap is one of the most important factors of cap selection. Some liners withstand chemicals better then others, while other liner types tend to be better moisture barriers. Below is a list of commonly used liner types and brief descriptions.

Poly-Vinyl: A poly-vinyl film adhered to a white pulp paper backing. It is a good liner type for chemical resistance, mild acids, alkalis, solvents, alcohols, oils and aqueous products; not recommended for active hydrocarbons or bleaches.

F-217: a three-ply material. F-217 has a low density foam core between two solid layers of low density polyethylene. F-217 has excellent chemical resistance and low moisture transmission rate. F-217 also has good taste and odor resistance.

PS 22: A pressure sensitive foam liner with one adhesive side that sticks to the container with the pressure used to place the closure on the container. When the closure is removed the pressure sensitive liner remains on the top of the container.

Induction liner: A specialized laminate containing aluminum foil and a plastic heat sealable film that hermetically seals to a container through the use of a machine that produces an electromagnetic current which releases the foil lining on to the container achieving a tight seal. Induction liners are available with pull tabs and peelable versions so not to leave residue on the container once removed.

Foamed Polyethylene: A good general-purpose liner material. It has a broad application base, chemical resistance, good for acids, alkalis, solvents, alcohols, oils, household cosmetics, and aqueous products. It is fairly poor use with for hydrocarbon solvents.

Poly-Seal cone lined™: Made out of LDPE plastic, the poly-seal cone lined cap provides a wedge type seal that not only seals across the top of the container, but also seals across the inside diameter. This liner is stress crack resistant and offers superior torque retention and excellent sealing characteristics. This liner is commonly used for liquid products. This liner should be tested first to make sure leaking does not occur.

Teflon Faced Foamed Polyethylene: A teflon lined foamed polyethylene that has excellent chemical resistance of teflon with the compressibility and sealing properties of polyethylene foam. Typical uses of teflon faced foamed polyethylene include: analytical lab samples, high purity chemicals, strong acids solvents. Uses include: environmental samples, pharmaceuticals, and diagnostic reagents.

Pulp Metal Foil: A polyester film laminated to aluminum foil, bonded to pulp board. Pulp metal foil liners have good barrier properties, as well good resistance to hydrocarbonates, oils, ketones and alcohols. The pulp metal foil liner is not recommended for acids or alkalis.

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