Traditional iron shafts feature a constant weight profile - shafts with the same mass properties throughout the set. With ascending mass shaft technology, the weight of each shaft increases by 3 grams throughout the set (long iron to short iron). Most golfers already use ascending weight shafts in their driver, fairways, and hybrids.
The new Titleist AP irons feature ascending mass stock shafts in distinct weight ranges matched to the performance of each model, with lighter long iron shafts for launch and speed and heavier short iron shafts for control.
Shaft Performance Guide