again, if you would use the search feature at the top of the page you could answer these questions for yourself (it's all been asked before, i promise). BS refers to the distance (usually in inches) from the mounting surface on the inside of the rim to the outer lip of the rim. more BS means the rims will sit closer in towards the body of the jeep, less BS will put them further outside the flares. so, BS isn't a physical item you can install. you may be thinking of wheel spacers which allow you to move your wheels further outside of the flares, which are as easy to mount as removing/installing a tire.
1995 4.0, AX-15, NP231(SYE), double cardan D/S
4.10 D30/D44-Detroit, 3.5" Superlift
Foothill Offroad u-bolt flip, K&N drop-in
MORE no-lift greasables, 1" BL, 1990 rollbar
33x12.50 retreads/steelies, Herculined
AtoZ rockers, no sway/trac bars, 40mm "console"