8 thru 10 Speed Road/MTB cassettes and 11s Shimano MTB Cassettes - Use the included 1.8mm wide spacer
All 7 speed cassettes - Requires a 4mm wide spacer (NOT included) plus the 1.8mm wide spacer.
Hub bodies made with a Shimano/SRAM spline pattern have three variations:
7 speed hub body splines are approximately 28mm wide, and thus the cassette is the same width.
8 thru 10 speed road hub body & 11s Shimano MTB splines are approximately 33mm wide, so their cassettes are correspond to that width
11 speed road hub body splines (like this one) are about 34.8mm wide, so their cassettes match that.
An 11s hub body can accomodate all the cassette speed varieties. Using less than 11s simply requires eating up the additional hub body space using spacers not occupied by a cassette. 11s hubs are a fairly universal system to accomodate nearly all cassettes you'd likely encounter. Exceptions to this rule are Campagnolo cassettes, and SRAM XD driver cassettes. Campy cassettes and XD driver cassettes are NOT compatible.