  The realization of tractor bundles as associated bundles in conformal
geometry is studied. It is shown that different natural choices of principal
bundle with normal Cartan connection corresponding to a given conformal
manifold can give rise to topologically distinct associated tractor bundles for
the same inducing representation. Consequences for homogeneous models and
conformal holonomy are described. A careful presentation is made of background
material concerning standard tractor bundles and equivalence between parabolic
geometries and underlying structures.
