The belt is a dart holding device used in some blasters.
A belt, like the chain before it, is composed of several barrels that can be or are linked together (depending on the belt). They are fed into the compatible blaster and are expelled out of the side of the blaster. Some belts may have air restrictors in each barrel.
Currently, the only Nerf blaster that supports the use of a belt is the Vulcan EBF-25, which accepts the only belt introduced as of yet, the twenty-five dart belt. The prototype version of this blaster, the Vulcan BF-50, featured a fifty dart belt. However, like the fifty-dart drum, it was never released.
Relationship to chains
It is considered a successor of the chain, from which it was partly based upon. There are many similarities between belts and chains, which explains why they are so closely related. Chains can be linked, but Vulcan belts can't without modification.