Stuck seat posts and chain widths

Another point to make with 9

Another point to make with 9 to 12 speed, is that that due to the narrower spacing between the sprockets on the cassette, the plates of each link are narrower each time you go up a gear option. This is how they have managed to get all the sprockets in 12 speed to fit in almost exactly the same space as 9 speed (although the 11sp+ HG/universal freehub body is 1.87mm longer than the first edition).

The thickness of the teeth profile will be uniform across 5-8 speed and 9 to 12 speed. This chart might need updating with road now being 12 speed and there are some 13 speed options out there (Rotor, and Campagnolo Ekar).

Unlike the rear, where the jockey wheels apply pressure to shift from the inside of the links, the front derailleur pushes the chain from the outside to move it, using different speed equipment can lead to slower and a little more imprecise shifting because of those subtle differences.

Apparently not all chain

Apparently not all chain manufacturers follow the same rules, eg in the 5-8 speed range you could find widths from 7.1 to 7.8 mm. Then 9 sp might be 6.7 mm, 12 sp 5.25, ie slightly different than in your table.

That’s why the speed number or range of speeds can vary for each chain, I guess.

So while the narrower chain should fit cassettes with less speeds, it might be more expensive, or not last as long… (I wanted to buy a Sram 12 sp for my 11 sp Shimano after reading excellent results, half the wear compared to all other chains, but they are also 2 x the price, so I just bought a chain checker instead for 7 €, and will keep using and monitoring my Shimano and Connex chains! I also had good results with KMC…