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My friend's road bike has a Shimano 105 CS-5800 11 speed 11-28T cassette on Fulcrum hubs and I ordered her a replacement but an Ultegra CS-R8000 11-28T (because the derailleur etc is Ultegra but when she's brought the bike round I found that the cassette is a 105).
On the back of the box is this picture:

Before I open the box, does the picture of the road bike next to the circle with a diagonal "NO" sort of symbol mean it won't fit or it will fit?
Thanks.
It’s talking about the 1.85mm spacer.
Just replace like for like, I don’t think there will be a spacer fitted on the existing setup. They are only needed with the 34t cassettes as they cross over with MTB range so are slightly narrower so the spacer is needed to fill the gap.
IMO its not about fit but use of a spacer. Some casettes need a spacer behind the biggest cog others don't. You should most times easily notice if spacer forgotten(hard to tighten or more likely loose casette). Or added but not needed(smallest cog will be to far ou or not even catch on the hub.
It will fit. The box is saying that it won't fit an MTB free hub which is irrelevant as your friend has a road 11 spd freehub.
Thanks all.
I'll crack it open then.
👍😎👌