As far as I know its something you got on french bikes, to be honest I dont really know any more than that. Does it tighten up fine in a steerer tube? I suppose the difference is minimal and would have little impact on anything.
Maybe I will have a look on Sheldon Browns website as that seems a safe bet for all things technical or obscure.
I have two of these marked 22 and have been using them for nearly 20 years in two of my bikes with 1" threaded steerers. I think they are great, absolutely no problems and they still look like new.