Maybe I got a bad one but mine isn't 8mm but 8.08-8.16mm (measured with vernier calipers) depending on where you measure. This means it is difficult or impossible to insert a wrench into some screw heads. I wanted to use it to remove the cranks on my bike. It works well with the crank bolts but will not fit the ISIS crank removal tool which also requires an 8mm allen key. The chrome plating seems to peel off easily and is probably the reason for the extra thickness. The wrench seems to bend easily, even with aluminum screws, and the workmanship isn't very good for such an expensive wrench (I could get a similar wrench a lot cheaper locally. I bought this tool online and it cost me the same money, it return). how much it costs to buy a new cheaper 8mm allen key so I'm keeping it to myself. Overall it's overpriced. Not recommendable.