Currently it's still the 3 studs, but it will change to 6 with a new casing. The main point is that those 3 studs are no longer disturbed when changing the filter (as they were previously,) as the housing is attached to the flange by 6 bolts and it is they that are removed. Additionally, should one of those bolts fail then the design is such that no leak will occur. It is a big improvement.