Seems that some steering columns have a square shaft at the lower end and some have a hex...
I also read that there are at least three part numbers for this joint, so it seems to have undergone at least two revisions in it's life-cycle.
If you look at the joint currently in your car, you might be able to spot if it's a square or hex shaft as the shaft extends through the joint a small amount... (this image is upside-down - upper shaft is at the bottom)
Images from drive2.ru