Don't know if there is such a thing as m11. However, have you thought about an SAE thread? That way you might not be making shaft a full 2mm smaller.
Yes but I've dealt mainly in metrics my whole life. I started out on honda automobiles and jumped to kawasaki and honda and yamaha atv's. Even my polaris atv I've used metric sockets on and they are supposed to be american made yes? If anyone can tell me the next SAE thread size smaller than a 12mm I would appreciate it. I would only be going 1mm smaller unless I have to jump down to a 10. How much smaller is the next SAE size down compare to metric?