Arguably the most popular tool in cycling.
When making adjustments to your bike, the three most common hex sizes are 4, 5, and 6mm. Park Tool, being the savvy purveyor of bicycle repair equipment that it is, developed what's quite possibly the most iconic shop tool ever -- the 3-Way Hex Wrench.
Known internally at Park Tool as the AWS-1, and to mechanics worldwide as a 'Y-wrench,' this three-way has 4, 5, and 6mm hex wrenches. Each are bonded to a sturdy plastic center handle in order to ensure a firm grip. And by having three sizes instantly available, you'll spend less time fumbling around, and more time fixing things.