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.
Postcards Postcards must be rectangular to qualify for First-Class MailÂ® prices. Oversized postcards will be charged as letters or large envelopes. Size Requirements: Height: 3 1/2 min. / 4 1/4 max. Length: 5 1/2 min. / 6 max. Thickness: 0.007 min. / 0.016 max.