bottom bracket refacing
A lot here depends on the &quot;shape&quot; of the imperfection.
I'd be looking for contact around something like three fourths of the circumference.
If you have contact most of the way around the shell, with a little &quot;divot&quot; gone so there isn't contact in one small area, it's probably not worth facing .5 mm off the shell to get contact on that last little bit.
On the other hand, if you basically have a &quot;point&quot; sticking out on one side, and essentially the entire rest of the shell is .5mm away from contact with the face of the shell, it's almost certainly worth cutting that spot down to get contact around most of the shell.
If it's a matter of the shell having been cut off slightly crooked, so the face is flat, but not square with the threads, I'd face it off so there was contact at least half (and as I said above, preferably more like three quarters) of the way around.