Is it possible to use an SRAM cassette PG 730 7-speed cassette with a Mavic FTS-X freehub? According to the spec, no spacer is required for an 11-speed cassette and for 9/10 speed version a spacer is required. I'm a bit confused since the manual is kind of vague.
Some good guidelines are here, courtesy of Sheldon Brown.
Assuming you have the right freehub body for Shimano/SRAM-style cassettes on the FTS-X, you just (probably) need a 4.5mm spacer behind the cassette.