Them SAS modules...

[xoknight]

Ok, I have been playing this game for about... 9 months and I still cannot find what is the difference between the Advanced SAS module and the inline SAS module.

Its just one is heavier (and slightly taller) than the other.

[Yasmy]

Those parts used to have different functions. Now they both just provide torque.

Use the lighter one. Some day they will get around to eliminating one of them,

or converting into something with a different function.

http://wiki.kerbalspaceprogram.com/wiki/Stability_Augmentation_System

[Kasuha]

Its just one is heavier (and slightly taller) than the other.

Together with slightly different look that's all the difference there is at the moment. They both were left in game to not break old ship designs.

[federally]

Or you get the stock rebalance mod and give them both purpose.