Rear Axle Hub Key

[29er]

I'm assembling my rear hubs after taking them off to grease the wheel bearings. I wasn't paying much attention when I removed the keys, but now notice each one has a chamfered end.

What is the correct way to install the key on the axle? Where does the chamfered end belong: facing up or down; toward the end of the axle or toward the differential?? How far into the threads of the axle does the key extend? Pictures would be helpful.

Many thanks!