Yesterday, I asked if anyone knew what a “Three Lens” was because it appeared in the Product Schedule page of the US Mint’s online catalog. User Mint News Blog said that the boxes the Mint sells to store proof coins sets to accommodate the three cases used in the 2007 proof sets with 14 coins. Today, the Mint made this box available on their website.
I learned that the Mint calls the cases for proof sets “lenses.”