For standard scalpel handles No. 3 and No. 4. Made of surgical steel, sterile and individually packed in aluminum foil. Differ in size and curvature. Comes in pack of 10 blades.Each blade has a unique shape and number. Use Handle #3 for blade numbers 10, 11, 12 and 15.Use handle #4 for blade numbers 20, 21, 22 and 23.