A Frag Belt is an engineer-only permanent "enchant" to belts.
The recipe for this tinker is learned from Grand Master Engineering trainers.
This item shares a cooldown with other explosives, such as Saronite Bombs.
Note also that while the Cobalt Frag Bomb and Saronite Bomb both are described as having a 5' radius, the targetting indicator for the frag belt is much smaller than for the Saronite Bomb.
This has a casting time, but this ability is not interrupted by movement, and it can be used while moving.