Please see the photo below, these are the rear bayonet filters which fit the Nikon 16/2.8 fisheye as well as the 15/3.5 ultrawide and the exotic 13/5.6
Nikon confusingly calls these 39mm Rear Bayonet Filters and they shouldn't be confused with the 39mm Rear Filters for long telephotos - it took me ages to find the red because of this. I'm looking for a good way to store them. Most filter wallets are far too big for these little things as they're designed to accommodate filters up to around 80mm. Nikon actually makes a special pouch called the "CA-2". There's one on ebay:
£24 shipped is a little expensive, so I'd like to hear any suggestions as to how I could store these is a safe way. Thanks!