I have a few of the other smaller pins as well. I don't think there would be any issues using the smaller pin, but have heard enough bad stories to turn me off it.
I personally don't think it's worth the risk for $10 (or half that in pounds).
I did order the 24mm pin and that is too big as well.
I think it may be 23mm (same as the CBR250RR I think). Could even be 21mm.
Might order that as well and see how I go.
I've almost got a whole set now haha.

Did you ever find the right size?

Hey mate,
Sorry didn't end up ordering the 23mm.
I will order it now and get back to you on it.

Alright well it's not the 23mm either.
Looks like I'm gathering quite a collection here.
I will have to find the other sizes I have and try them out before I order anymore.

i use a long 19mm socket over my undersized pin to give a bit more height to clear the underside of the nose cone

Was 23 too big or too small?