Where would one get a 17/64 box wrench?

It's either metric or very crappily made SAE hex. This is what we get for outsourcing everything and one more reason why I always rebuild original factory wheel cylinders.

I'm sure you are correct on the crappy manufacturing tolerances.

Here you go! A 17/64 ignition wrench:

http://www.globalindustrial.com/p/tools/Ratchets-Sockets/Wrenches2/3122-ignition-wrench-17-64-x-19-64

ocdart found the same thing I did, but at a different supplier: http://www.mscdirect.com/product/details/85380517

If it's for bleeding brakes with a chinese brake cylinder that nothing fits, I'm pretty sure I ran into that and got this 7mm to work:

http://www.amazon.com/dp/B000N322Q4/?tag=joeychgo-20

Sorry guys, I wouldn't advise using a ign. wrench on a brake bleeder. Those wrenches are stamped steel and don't have much strength. They would spread easily and round off the bleeder. They are designed to loosen machine screws. You would be better off using a adjustable wrench.