Just because you can use a 5/16 wrench on an 8 mm nut sometimes has nothing to do with the threads involved. There's a lot more going on than just the external sizes and wrench sizes. The threads are not the same between Metric and SAE. So from now on don't even think of using anything other than Metric on your bike. Even if you are attaching something extra or a fairing or anything like that. When you go to the hardware store and look for nuts and bolts make every effort to only use Metric fasteners.
There may be something someday that comes up where you are forced to use some SAE fastener on your bike. It's OK. But only if there's no way around it.
You'll thank me later. (Monk)