Originally Posted by
fietsbob
older cassettes were held together with 3 long thin bolts, so could be .
newer ones there is a bigger sub assembly and only a couple small cogs are loose
I believe the "spider" mounted cog clusters started at 9-speed.
Yes, you can substitute a couple of 7-speed cogs in an 8-speed casette but be sure to use 8-speed spacers. Shimano 7-speed cogs are 1.85 mm thick and 8-speed cogs are 1.80 mm thick so the difference is minimal.