Park Tool AWS-3 Hex Wrench
The AWS-3 3-way hex key is made of Bondhus Protanium high torque industrial steel and is heat treated for a long life. The tips are chambfered for the perfect fit, every time.
I once cut my leg on one of these. That's not the tool's fault, though. The tool is a good tool. Signature three way comfort and long lasting steel tips for the drivers. Good tool.
With this, the other Park hex 3-way wrench, and the 3-way Torx wrench, you can tighten or unscrew 90% of bike bolts. I highly recommend having all three in the maintenance kit!