Z Blades- These innovative blades will remain flexible and retain their sharpness much longer than the average cold knife blade. The grinding of the blade is at a greater angle than other cold knife blades. This makes the resistance less when pulling the cold knife to cut the urethane. The end result is a cold knife blade that has the ability to resist breaking, last longer and keep a sharp edge. Equalizer produces two types of cold knife blades. Both the standard and the coined blades use the same proprietary hardening process. The Coined Z Blade... A coined cold knife blade has the cutting surface of the blade made thinner, only about 35 thousandths of an inch thick. A normal cold knife blade is 62 thousandths thick. Many technicians routinely grind standard cold knife blades thinner so they will cut easier. Sometimes this grinding will overheat a blade and damage the hardening. Z blades are thinned before they are hardened so there is no need to grind them thinner. Should I buy coined or not coined blades? If you use a cold knife blade right out of the box and never grind it thinner, then use the standard thickness Z1, Z2, Z3, or Z7. If you like to take a new blade and grind it thinner before you use it, then you should purchase Z4, Z5, Z6 or Z8. Made in USA.