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I save my hotel key cards and keep a few of them in each of the safety cabinets and kits.

You can hold up a key card to cover each bayonet filter and it seals it perfectly for a quick test at any time.

I usually put those in a parts drawer for use when opening electronic devices built with clipped together plastic cases.

Good tip, though! I'll have to try that next time I'm using the bayonets.