Nikon CA-2 Case and Filters Questions

I bought a box of Nikon cameras for $9 and found a few Nikon CA-2 filter cases each with these three filters in it. They are quite small and all appear to be unused. I tried doing a little research but can't really figure out what they are use for. They are a little over a 1.25 inches total width and are labelled A2, B2 and 056.

Anyone familiar with this small of a filter?

These were used on wide angle lenses, such as the Nikon 13mm, 15mm, etc. AI lenses. These filters fit on the bayonet mount of the lens, not on the front as you would expect.

Is this kit for sale? I have a 16mm nikkor that I got used without the kit. Would be interested in purchase.

Kat
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