In the post-office today I saw this piece of board that's used as a size-template to quickly assess which envelope to choose. This is a formalized version of the same tool that I used for the many years that I spent cataloguing and packing Sanskrit manuscripts at the Wellcome Library in London. I made a piece of board with three main size-outlines, for MSS of α, β, γ sizes. Anything larger than γ counted as δ. Palm-leaf MSS were all ε.
It was nice to see the same tool being used for a similar job, in an Austrian post-office!