It would depend on the diameter of the bracket. Say for instance if a certain bracket either hand made or factory is say 1" wide, I would not go anything over 1/2" directly in the middle and of course this all depends on what duty that specific bracket has to do. If it's a sensitive part where something may/is hanging on the limb, then even a smaller 5/16" hole or maybe even nada. I personally prefer to make sensitive brackets out of 6AL4V Titanium and other non-sensitive brackets out of Aluminum either in 3003 which is malleable or 6061-7075 if it's a flat bracket needing strength.
I have at times asked of a 90% bend from 7075 or even 6061 Aluminum and came up short with a crack or a weakened crease. I'd rather carry more weight than to be sorry. Certain Dogs should be left sleeping. Be careful out there and re-think all that is being done with hindsight. I take second looks, first time.
Aluminum also likes to work harden itself, so keep an eye on things while going through your multi-point safety check before the races.
