Messing around and made up this.
Its about 332mm long and 120mm wide.

Good for opening letters?

Print this on edge (22.5 degrees) for best results. See comparison pic to see why).

*** check out the newer one:
https://www.thingiverse.com/thing:3053526

Say thanks by giving OldGaf a tip and help them continue to share amazing Things with the Thingiverse community.