This site claims, the Franks "derived their tribal name from the name of a type of spear that they used."
I know, Hanks & Hodges write this in their Oxford Dictionary of First Names, but I can't find anything in any of my German books (Förstemann, Kaufmann, Bach, Seibicke); they all agree on the Germanic word *franka, brave (which later took the meaning "free").
Can anyone back up the spear-theory with anything beyond H&H?