suffix (for the FCT series)

A letter (e.g., A, B, C), immediately following the device number, that indicates the speed grade for the device.

NOTE 1 For example, FCT244A refers to the "A" speed version of the "244" function with CMOS output swing, and FCT244AT refers to the "A" speed version of the "244" function with TTL output swing.

NOTE 2 The slowest speed grade has no such suffix.

References: 

JESD18-A, 1/93