Mechanics and Fixing Any Questions Answered

Should have a 1mm spacer assuming it's a 9/10 speed hub.

9/10 speed freehub:

9 speed cassette, no spacer
10 speed cassette, 1mm spacer

9/10/11 speed freehub:

9 speed cassette, 1.8mm spacer
10 speed cassette, 2.8mm spacer
11 speed cassette, no spacer