discovery 2 wheel bearing differance

Hi does any body know the differance with a front and rear wheel bearing for a disco 2,apart from being front and rear.as have just changed one on the front and it is now giving me three amigos and it was ok before.checked the abs sensor and thats ok.i seem to remember the old bearing having differant abs notches in it and not notched all the way round like the one i have fitted.i cant find the old one to compare as i think ive thrown it by mistake.