Plastic cap 18/410, black

The plastic cap 18/410 is a simple screw closure for bottles and vials with an 18/410 neck finish. It serves one basic purpose: reliably sealing packaging containing serums, oils, tinctures or tonics so the contents do not spill and are not unnecessarily exposed to air. It is suitable wherever dropper or spray dispensing is not required, but a secure seal is — for example on stock bottles, samples, transport or storage of intermediates.

The black colour of the cap complements brown, blue and clear glass well and has a neutral appearance that does not interfere with the label or the overall look of the product. The cap is suitable for use with cosmetic products; the declaration of conformity and related documents are available with the product.

What the 18/410 designation means

The thread designation is the key to ensuring the cap fits the bottle. The number 18 indicates the outer diameter of the neck finish in millimetres; the number 410 describes the thread profile — the height of the neck and number of turns. The cap therefore fits exclusively on packaging with an 18/410 neck finish, not on similar neck sizes, even though the difference is almost invisible to the eye.

Bottles and vials with this type of neck finish, as well as ready-made combinations of container and closure, are available in the Handymade range. When creating your own combination, we recommend verifying the seal integrity with the specific formulation, especially for thin or volatile contents.

Use in formulation and packaging

• Stock and storage bottles – a secure closure without a dispensing element is suitable for oils, oil serums, tinctures and in-progress phases that are poured or dosed during further processing.
• Samples and testers – small vials with a cap are practical for test batches, comparing formula variants or samples for customers.
• Replacement for a dropper or spray cap – if you are transporting a bottle fitted with a dispensing closure, seal it with the plain cap for the journey and attach the dispensing element at the destination.
• Anhydrous and aqueous contents – polyethylene is resistant to water, ethanol and vegetable oils, so the cap can be used on tonics, hydrolats, tinctures and oil blends.

Good to know

Before first use, wash the cap and, if needed, disinfect with isopropyl alcohol or ethanol and allow to dry completely. Polyethylene deforms at elevated temperatures, so do not sterilise by boiling or in an oven; chemical disinfection is sufficient.

When filling the bottle, stop at the nominal volume, not to the brim. The nominal volume of the container already accounts for the headspace needed below the neck for the cap to seat properly and for the contents to expand with changes in temperature. An overfilled bottle will easily leak once the cap is tightened.

Tightening by hand is sufficient — gentle and even. Excessive force will not improve the seal but may damage the thread or deform the rim of the cap. If the closure 'clicks over' after tightening, the thread does not match and the neck finish is likely a different size.

Essential oils and solvents in concentrated form may affect the surface of plastic on prolonged contact. For neat essential oils or blends with a high proportion of solvents, we therefore recommend monitoring the behaviour of the cap over time or opting for a closure with a liner designed for such contents.

Reuse is possible provided the cap is undamaged and can be thoroughly cleaned. For products intended for sale, a new closure is always recommended. Used caps should be placed in sorted plastic waste collection in accordance with local regulations.

Frequently asked questions