Originally Posted by timcupery
I thought the main reason for a shim was to use 11t small cogs on older freehubs that had splines that were too long so the cassette needed to be set further outboard. But I'm not familar with various botique wheels.
In this case the "shim" is the 4.5 mm spacer needed to use a 7-speed cassette on an 8/9/10-speed freehub body.