Originally Posted by Frogtop
Yep, as referenced to a mill file or a safety file. Its all about the way the grooves are set on the file. A bastard file is more aggressive than a mill file and a safety (I'm sure there is another name) has no grooves on the edges to protect close work. If memory serves the bastard has crossed hatched grooves and the mill's are all parallel. As per usual, I sure there are more variations and that we have colleagues more familiar who will enlighten us - please.
this is correct info. A bastard file has cross hatched teeth and cuts aggressively and quickly, but leaves a rough cut. A Mill has parrallel teeth on an angle and makes a smooth even cut.