One of the things that tires you out when you're riding on the road is vibration from rough pavement. Bontrager's Bzzzkill Harmonic Dampers go inside your handlebar ends and utilize harmonic damper technology to cancel these high-frequency vibrations so you don't feel them and can ride more comfortably. The Bzzzkills have small weights held between elastomers. When you're riding over rough roads, the elastomers delay the oscillation of the weights, canceling the vibrations so you don't feel them.
Bzzzkill Dampers come in 32- and 76-gram models. This is the 76-gram model and it's for rough roads.