Applicability of the New Rules. The new cargo securement rules apply to the same types of vehicles and cargo as the old rules, covering all cargo-carrying commercial motor vehicles (as defined in 49 CFR 390.5) operated in interstate commerce.
Most commercially-produced postcards measure approximately 4.21 inches by 5.47 inches. Less commonly, smaller postcards are typically 3.5 inches by 5.5 inches, close to the minimum size the USPS allows.
All in all, a 5-inch by 8-inch postcard or a 6-inch by 9-inch postcard is large enough to stand out from the standard 4-inch by 6-inch postcard pack, so simply adding a few inches can be just the trick you need to put your return on investment over the top.