Six-dimensional (1,0) SCFTs on the tensor branch have an interesting spectrum of BPS objects consisting of self-dual strings and their bound states. The BPS strings can be thought of as the instantons for the 6d gauge group, and are building blocks for computing 6d supersymmetric partition functions. The goal of this talk is to rephrase their properties from the point of view of a worldsheet N=(0,4) NLSM. This perspective shows that self-dual strings of arbitrary 6d SCFTs share several universal features, and leads to a better understanding of their spectrum and of their global symmetries.