Advanced Oster® Cryogen. Oster A5 blades are the gold standard in detachable blades, combining tough anti-micorbial protection with superior hardness for the ultimate in performance and value. Oster® Cryogen -X Agion® blades have advanced, silver based Agion antimicrobial portection built in, to prevent the growth of bacteria, mould and mildew on blade surfaces. Size 40 blade has a 0.25mm blade cut. This is best used for very close clipping.