This is all I have ever seen on the SB oil filter plate. They are usually tight so if they did have thin flats on there I would still use the square 3/8" drive to turn it out first. http://www.manciniracing.com/moenoilfimof.html
I've seen the one that the OP's talking about with the thin depth hex on the outside. I hate those f*ckers as there isn't enough meat on the hex to get them off if they are tight... :banghead: :banghead: :banghead:
Some of the newer ones have a deeper hex than the old ones..