Although airsoft guns in the United States are generally sold with a 6mm (0.24in.) or longer orange tip on the barrel in order to distinguish them from real firearms, this is not required by federal law. Manufacturers and importers may cite Part 272 of Title 15 of the Code of Federal Regulations on foreign commerce and trade (15 CFR 272), which stipulates that "no person shall manufacture, enter into commerce, ship, transport, or receive any toy, look-alike, or imitation firearm" without approved markings;[37] these may include an orange tip, orange barrel plug, brightly colored exterior of the whole toy, or transparent construction.[38] However these restrictions do not apply to "traditional B-B, paint-ball, or pellet-firing air guns that expel a projectile through the force of compressed air, compressed gas, or mechanical spring action, or any combination thereof." [39] This language exempts airsoft guns from these requirements, placing them in the same category as bb-guns, pellet, air, and paintball, none of which are conventionally sold or used with an orange tip, and many of which bear as much resemblance to real firearms as airsoft guns do.