length of hash name

[Dan Muey]

Anybody happen to know off the top of their head what the max length of characters is 
that a hash's name can be?
 
EG ::
 
%123456789 = (); is a nine charcter name
%joe_mama_said_to_tell_you_hi = (); is a 28 character name 
etc..
 
Thanks
 
Dan