In a nutshell, O1 steel is easy to hone and a very fine edge achieved relatively quickly. A2 steel takes a little longer to sharpen but retains its edge for longer. To add to the mix we now have the highly acclaimed PM-V11 alloy blades that are easier to sharpen than A2 and hold an extremely durable cutting edge for up to twice as long as A2. What does this mean in practice? If you’re roughing something to size or planing abrasive exotics then PM-V11 or A2 are probably the better choices. However, for fine finishing or the pure pleasure of working with the very sharpest of tools, go for the O1 option. 3.2mm(1/8") thick, lapped blades, 12.7mm(1/2") wide.