Are spacers needed between Ultegra 9/10 freehub and a 9 spd cassette?

[Louis]

Just got my first bi-sexual freehub (Ultegra FH-6600, 9 or 10 spd). In the directions they show you that some 10 spd cassettes require a spacer between the freehub and the cassette, but some do not. However, they don't provide any information about spacers if you are using a 9-spd cassette.

Other than trying it, how do I figure out if I need a spacer or not, if I'm going to use a 9-spd cassette with a 9/10 freehub?

TIA
Louis

[CNY rider]

I do not use any spacers with 9 speed cassettes on that hub.
So far, so good......

[Big Dan]

6600 and 9 spd. No spacers on mine.

[Louis]

Thanks guys. Looks like I don't need a spacer.

Louis