Seems like a good place to mention that I bought a Klein bottle hat from Cliff for my (mathematically inclined) wife for Christmas and she loved it. Also there

Seems like a good place to mention that I bought a Klein bottle hat from Cliff for my (mathematically inclined) wife for Christmas and she loved it. Also there is more to it than just the item, the packaging and other extras really put it over the top. I can't recommend it enough.