I thought I had this all wrapped up, but I learned something new today.
So I have 2 sets of wheels for my general purpose bike.
All 10-speed.
The original cheap Shimano R500, shod with M+ which I use in winter.
The R500 winter wheels have just had a new Ultegra CS-6700 cassette installed, and the indexing is sweet.
I also have a pair of Mavic Axiums which were supplied with my carbon bike, but surplus to requirement.
They have a cheap Tiagra-level CS-4600 cassette on them.
So I use these as 'summer' wheels on the general hack bike.
Nice day today, so I decide it's time to swap the wheels.
The indexing was fairly shit, but I didn't adjust it on the road, because I planned to swap the nice shiny cassette onto the nicer wheels when I got home.
So the Mavic wheels with shit indexing had the mavic 1.75mm spacer, but no shimano 1mm 10-speed spacer.
Usually, both are required.
I cursed the person who assembled it, and fitted the new Ultegra CS-6700 with both spacers as $deity intended.
All is sweet.
So I go to put the Tiagra CS-4600 onto the R500 wheels.
I find a 10-speed spacer, and assemble it.
But I can't. Google shimano tech docs.
The CS-4600 does not come with a 10-speed spacer, and cannot be used with one.
The 8 largest sprockets are all riveted together with 3 big long rivets.
The heads of the rivets are where the spacer would be, and act as a spacer themselves.
You can't add a 1mm 10-spd spacer, because it then sits too far out.
Now, this would be just fine and dandy, if the rivet heads were actually the same thickness ( 1mm ) as the spacers.
But they are not.
They are only about 0.5mm.
These Tiagra 10-speed cassettes don't sit in the same place as higher-grade cassettes with spacers, and it is enough to fuck up the indexing.
Highly tempted to grind off the rivet heads, and use a normal spacer.