This release of trigger shifters features SRAM's Impulse Technology, which offers "optimized ergonomic advantage that allows you to shift with whichever impulse you choose."
Impulse? Thumb, finger or knuckle.
The 2004 version of the shifters have new housing units, new Impulse Technology internal components, Integrated gear indication, a new index mechanism and a "StraightShot" cable change path.
There are two types at two price points:
1:1 actuation ratio - ESP. X-9 (priced at just under XT) and X-7 (priced at just under LX).
1:2 actuation ratio - other systems, Rocket (priced at just under XT) and Attack (priced at just under LX).