Disposable Carbon Steel Surgical Blades, Sklar, #21. Sklar's Disposable, Sterile, Carbon Steel Surgical Blade #21 is a larger version on the #10 Scalpel Blade. It has a curved cutting edge and a flat, unsharpened back edge. The #21 blade is smaller than the #22 blade and larger than the #20 blade and is compatible with the #4 series and larger handles. This blade is one of the most traditional, commonly used blades and often used for making small incisions in skin and muscle. Disposable blades are available in bulk quantities of 100 per box.