  Tensor harmonics are a useful mathematical tool for finding solutions to
differential equations which transform under a particular representation of the
rotation group $\mathrm{SO}(3)$. The aim of this work is to make use of this
tool also in the setting of Finsler geometry, or more general geometries on the
tangent bundle, where the objects of relevance are d-tensors on the tangent
bundle, or tensors in a pullback bundle, instead of ordinary tensors. For this
purpose, we construct a set of d-tensor harmonics for spherical symmetry and
show how these can be used for calculations in Finsler geometry.
