Apr. 1, 2015. TDK Corporation has announced that its Hong Kong-based HDD head manufacturing wholly owned subsidiary, SAE Magnetics (H.K.) Ltd.
You use a wrench to screw, or unscrew a bolt. A screwdriver is for screws. Either way you turn it left. Some bolts have reverse threads and would turn the other way to unbolt.
You're trying to prevent the bolt nut from turning, thus unscrewing. The jagged side will, to a small degree, bite into the metal of the bolt to increase the holding power. (The majority of the holding power is from just the compression of the lock washer.) Turned the other way will work, just not quite as well.