I was torn between ordering the smaller 8mm, this one or the larger 14mm. I'm glad I got this size for my needs. I added one to the back of the drill (after making sure it was level when the tip of the drill was straight) and now I can drill a lot more straight holes than ever before. ok but they don't have straight back ends so i have to bend a piece of metal as a spacer to get the correct bubble level. I also think I'll add one or two to the mounts on my portable table saw and table router. I have no idea if they are entirely "true" but they sure get you "close" to the level and are the perfect size to add just about anything you want close to the level quickly .