I am getting ready to order some Zephyr slotted insert bits and I am trying to decide between the two hardness options they offer. The "X" grade is harder and is meant for hard sheet metal screws and self tapping screws. The "A" grade is not as hard and they recommend it for regular machine screws. I was planning on going with the "A" grade bits since I planned on mostly using them for regular screws, but I got to wondering if there would be any downside to selecting the harder "X" grade bits. The harder bits would hopefully resist wear better, but I suppose they would be more brittle. Does anyone have some better insight as to what would be the disadvantage to the harder bits?
