Paolo,

What they are saying is that the nut set you have is just like the one at[link=http://www.horizonhobby.com/Shop/ByCategory/Product/Default.aspx?ProdID=TRU0822]Saito tru turn nut set[/link]. This designed to fit Tru Turn metal spinners like this [link=http://www.horizonhobby.com/Shop/ByCategory/Product/Default.aspx?ProdID=TRU2502B120]one[/link], which are held together by a bolt that goes in from the front of the spinner. The bolt screws into the small hole in the long prop nut when they are installed on the engine like you have them in your pictures.

If you don't want to use a tru turn spinner, you don't have to. As long as the tru turn nuts will fit inside the spinner you want to use, you should be ok.

Good luck,
Duke