18 CFR §154.103

1. (a)The tariff must contain sections, in the following order: A table of contents, a preliminary statement, a uniform resource locator for the Internet address of a map of the system, currently effective rates, composition of rate schedules, general terms and conditions, form of service agreement, and an index of customers.
2. (b)Rate schedules must be grouped according to class and numbered serially within each group, using letters before the serial number to indicate the class of service. For example: FT-1, FT-2 may be used for firm transportation service; IT-1, IT-2 may be used for interruptible transportation service; X-1, X-2 may be used for schedules for which special exception has been obtained.