[Gubi]

Yeah, I think Fraz is a little confused in his terminology. The "arm" is the part attached to the car - you don't replace those. The blade (metal piece with the rubber wipe) snaps on to the arm and can be bought at your local auto parts store, usually with adapters for a variety of arm types. You can also buy just the insert, which is just the rubber piece that slides onto the blade.

Usually you can just replace the inserts to save $, but if that doesn't work for you replacing the whole blade makes sense. You never replace the arms unless they break.