Some main crankshaft bearing cap nuts are actually 12 pt nuts. Some driveshaft universal joint attaching c- clamps are fastened sing 12 point nuts. For these applications you will need to use a 12 point socket or box wrench end. If you attempt to remove these with your 6 point sockets by hammering them on, you will trash both your sockets and your main bearing cap nuts. If you attempt to use 6 point sockets with a breaker bar, you will have to walk half way around your project just to reposition your wrench. If you attempt to use 12 point sockets with a breaker bar, either you didn’t need to be using a breaker bar in the first place, or you will most likely round off the itty bitty tips of your nut. In either case, you should go get an impact wrench and 6 pt impact socket and loosen it the right way. And leave your chrome plated hand tools in that drawer where they never get used anyways. Maybe put them in your trunk tool box , where they might some day actually be useful. As for using 12 point sockets on square bolts: this can be accomplished using a large hammer to mash the 12 pt socket down on to the square nut, and it is a one way ticket only. They actually make a thing called an 8 point socket for square nuts. There also is a square socket for square nuts ( the difference between 8pt and square sockets is kind of the same as the difference between 12 pt. Sockets and 6 pt. Sockets). They also make crescent wrenches for square nuts and, you can use open end wrenches too.