Envelopes:
Horizontal
a 8.3 to 8.5 inches (210 to 216 mm)
b 0.25 inch (6.4 mm) -- Letter-size paper
3.4 mm (0.13 mm) -- A4-size paper
Vertical
c 11 to 14 inches (279 to 356 mm)
d 0.125 inch (3.18 mm)
e 0.3 inch (7.6 mm)
