I use them and the Grizzly heads. Take a few minutes to take the needle point off, and try sharpening on a 10" single cut file, by laying the file on a table, set the head on the file and pull head, or reverse file and push, taking care to retain the bevel. It won't take much to sharpen, then strobe with leather to remove burr, finish by pushing or pulling the edge of the file across the blade away from the blade. Done lightly, once or twice it puts a fine saw tooth edge on the blade and will cut thru a leather strap without much pressure. The toughest part is maintaining the original bevel.