Originally Posted by
HillRider
OK, Shimano 10-speed cassettes come with a 1 mm spacer that goes behind the largest cog. It is required on all Shimano 8/9/10-speed freehub bodies (the few 10-speed only hubs don't require it). A Shimano 11-speed freehub body requires a 1.85 mm spacer to accept 8 or 9-speed cassettes and the additional 1 mm spacer to take 10-speed cassettes.
And that is what turned out to be missing, a 1mm spacer.
Staked out the LBS. He opened at 10:00am and I was the first customer. He agreed that the spacer was needed. He put it on and I'm ready to go. $3.91. There was a lineup behind me.