These TRIPLE TIME STAMPING cards are popping up lately on Pinterest (like this one above from Angie Leach), and there are several wonderful videos out there to learn this simple technique. Here's one of my favorites below with the measurements written out for easy reference:
STAMPED: 2 x 3 1/4
MAT: 2 1/4 x 3 1/2"
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STAMPED: 3 x 4 1/4"
MAT: 3 1/4 x 4 1/2"
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STAMPED: 4 x 5 1/4"
CARD BASE: 5 1/2 x 8 1/2" folded in half