  Bright features (`knots') in extragalactic jets are commonly associated with
reheating of charged particles in regions with shocks or strong compression. We
find a natural appearance of nozzles in simulations of toroidally magnetized
jets, and propose this as a generic mechanism of knotted structures such as in
the jet of 0800+608. Nozzles provide correlated enhancement of emission in
radio and optical, such as discovered in HST observations of 3C273. The
simulations reveal a rich structure of knots, including a nose cone with a
propagating knotted structure and a hot-spot as the most extended brightness
feature. Unexpected is the observed separation of the hot-spot from a composite
Mach disk closer to the source.
