wheel help

hi people, in reference to my previous post about wanting some new wheels, i now know that i have to look for some et38 wheels to get the correct fitment, does this mean that if i got some et35's then the holes would be out of line or does the "et" bit just mean how far off the hub they sit???

also could someone please explain to me the breakdown of all the numbers on the wheels, eg  7x15,et35,4x100 etc, it just confuses me a bit,

thanks in advance

m333ksd

7is the width of the wheel, 15 is the height.
not sure exactly what the et is but think its how deep the wheel sits
4 is the number of holes and 100 the spacing of said holes.

et is the offset value which relates to how far the wheel sticks out.