The consensus seems to be that they use 22.2mm as their seatpost diameter.Here is another 22.2 mm diameter reference with JC as a contributor which makes it pretty much gospel. This was (is) a unicycle standard for some time. It’s not necessarily good or strong but it’s easy to get. If it will accept a standard United style saddle bolt pattern is the most universal also. This should accept a KH, Viscount, United, and several other saddle brands. The KH will be the most comfy of these. It is also the only one I know of with a front handle.