A1 Blank Cards (3 1/2 × 4 7/8). A popular size for reply cards, invitation insert cards, thank-you cards, and more. There are pre-cut and pre-scored A1 blank cards to complement your invitation ensemble. A2 Blank Cards (4 1/2 × 5 1/2). This size is commonly used as reply cards, postcards, thank-you cards, note cards, and many more.