  Recent studies have focused on the the role of initially weak toroidal
magnetic fields embedded in a stellar wind as the agent for collimation in
planetary nebulae. In these models the wind is assumed to be permeated by a
helical magnetic field in which the poloidal component falls off faster than
the toroidal component. The collimation only occurs after the wind is shocked
at large distances from the stellar source. In this paper we re-examine
assumptions built into this ``Magnetized Wind Blown Bubble'' (MWBB) model. We
show that a self-consistent study of the model leads to a large parameter
regime where the wind is self-collimated before the shock wave is encountered.
We also explore the relation between winds in the MWBB model and those which
are produced via magneto-centrifugal processes. We conclude that a more
detailed examination of the role of self-collimation is needed in the context
of PNe studies.
