Old wheels and new cassetes

[mr Mag00]

I have some old mtb wheels.
i am looking at buildig up a bike for my son.
is there a width of the freehub that will determine what speed casette i will be able to fit?
i think it was running 7 speed when i last rode it a 'few' years a go

 

[02GF74]

I think so. 7 was narrower to 8/9 speed - the 7 and 8 have the sprockets same distance apart so freehub has to be wider, and use same width chain.

9 speed are closer together so they fit onto 8 speed freehub.

dunno about 10 speed.

 

[ieperlee]

Not an answer, only a link to him, who knew not only the answers, but all the questions too.