Kilner® Wide Mouth Sealing Discs: What They Do and When to Replace Them

Quick answer

Yes, most Kilner® Wide Mouth Jar owners need spare sealing discs, because the flat disc is the part that takes daily wear while the rubber seal does the actual sealing. Buy the Kilner® Set of 12 Wide Mouth Sealing Discs if you use your jars often, replace any disc that is dented, warped, or scratched, and always match the disc to the jar size you own.

If you have ever lifted a Kilner® Wide Mouth Jar and found the flat metal lid bent, scratched, or faintly rusty, you have already met the reason this set exists. The sealing disc is the thin metal lid that sits on top of the jar, and it is the part most likely to be damaged, lost, or mixed up between jars.

This guide answers the questions people actually ask before buying the Kilner® Set of 12 Wide Mouth Sealing Discs: what a sealing disc is for, how it differs from the rubber seal, whether discs are reusable, and how to know which size fits.

What are jar sealing discs for?

A sealing disc is the flat metal lid that sits directly on the rim of a wide mouth jar. It holds the jar closed, protects the contents from dust and spills, and works with the rubber seal and the screw band to create an airtight closure. Think of it as the roof of the jar rather than the gasket.

On a Kilner® Wide Mouth Jar the disc is the part you lift off every time you open the jar, so it takes far more handling than the band or the seal. That is why discs are sold as replacement parts in multipacks rather than one at a time.

• Use a disc on every jar you close, even for dry goods like flour, rice, or biscuits.
• Keep one spare disc per jar size so a damaged lid never stops you mid-batch.

Kilner sealing disc vs rubber seal: what is the difference?

The sealing disc is the flat metal lid. The rubber seal is the soft ring that sits under the screw band and presses against the jar rim to keep air out. They are two separate parts with two separate jobs, and they wear out at different rates.

The disc can dent, scratch, or discolour, but a small dent usually does not break the closure. The rubber seal is the part that decides whether the jar is genuinely airtight, so a hardened or cracked seal is the more urgent problem. If your jar is losing its seal, check the rubber ring first, then inspect the disc.

• Replace the rubber seal when it feels stiff, cracked, or flattened.
• Replace the disc when it is warped, deeply scratched, or no longer sits flat on the rim.

Are sealing discs reusable?

Yes. A sealing disc is reusable for as long as it sits flat, is free from deep scratches, and shows no rust. Because it does not touch food directly in most setups, it usually outlasts the rubber seal by a wide margin.

The practical limit is physical damage, not a fixed number of uses. A disc that has been dropped, bent by over-tightening, or left wet for days is a disc that will not seal reliably, no matter how new the rubber ring is.

• Dry discs completely before storing them, even if they look clean.
• Retire any disc with rust spots near the rim, since rust spreads and pits the metal.

Which jar sizes do these discs fit?

The Kilner® Set of 12 Wide Mouth Sealing Discs is made for Kilner® Wide Mouth Jars. According to the product information, the sizes currently available for these discs are 0.35 litre and 0.5 litre jars.

That is a deliberately narrow fit. Wide mouth jars have a wider opening than standard mouth jars, so a disc from one will not seat on the other. Check the size printed on the base of your jar before ordering, and do not assume a disc that looks close will seal.

• Check the litre marking on the jar base, not the box it came in.
• If your jar is not 0.35 litre or 0.5 litre wide mouth, this set is not the right match.

How to use a sealing disc correctly

Place the rubber seal into the screw band first, then set the sealing disc on the jar rim, then screw the band down until it is snug. Over-tightening is the most common mistake because it bows the disc and can damage the seal underneath.

For dry storage, the disc alone plus a lightly tightened band is usually enough. For preserving, follow the processing method your recipe specifies and let the jar cool undisturbed before testing the seal.

• Stop turning the band as soon as you feel resistance, then give it a small final nip.
• If a disc keeps popping loose, check the band threads before blaming the disc.

How many discs should you keep on hand?

A set of 12 covers a realistic pantry rotation. If you keep six wide mouth jars in active use, you have a full spare set for the day a disc gets bent or a jar goes missing with its lid still on it. That is the main argument for buying a multipack rather than a single replacement.

If you only own one or two wide mouth jars, a 12-pack is more than you need right now, though discs do not expire. Match the quantity to how many jars you actually fill, not how many you plan to buy someday.

• Count your wide mouth jars first, then add two or three spares.
• Store spare discs stacked somewhere dry, not in a damp cupboard above the kettle.

Sealing disc quick reference

What the disc actually does

It is the flat metal lid on a Kilner® Wide Mouth Jar. It closes the jar and works with the rubber seal and screw band to keep contents airtight. If the jar is losing its seal, inspect the rubber ring before replacing the disc.

Which size to buy

The Kilner® Set of 12 Wide Mouth Sealing Discs fits Kilner® Wide Mouth Jars, with current sizes available being 0.35 litre and 0.5 litre jars. Measure or read the jar base marking before you order.

When to replace a disc

Replace it when it is warped, deeply scratched, rusting, or no longer sits flat on the rim. A disc that still lies flat and is undamaged can be reused. Keep two or three spares so a damaged lid never interrupts a batch.

Product facts worth knowing

• Kilner® Set of 12 Wide Mouth Sealing Discs: Designed to fit onto Kilner® Wide Mouth Jars, with current sizes available being 0.35 litre and 0.5 litre jars. Confirm your jar size before ordering, because these discs are sized for wide mouth jars only and will not fit standard mouth jars.
• Square Glass Clip Top Jar - 0.5 Litre: A durable 0.5 litre clip top glass storage jar with an airtight clip top, suitable for preserving jams and chutneys and storing dry foodstuffs. If you prefer a clip top closure instead of a screw band and disc, this is the alternative format for the same 0.5 litre capacity.
• Kilner® Herb Keeper Set: Keeps home grown or store-bought herbs fresher for longer, for up to 3 weeks. A useful reminder that not every storage problem needs a sealing disc, since some fresh items do better in a dedicated keeper.

Sealing discs are the inexpensive part that keeps your wide mouth jars working, and a 12-pack means you are never stuck because of one bent lid. Check your jar size, keep the discs dry, and treat the rubber seal as the part that decides whether the closure is truly airtight.