The center bore needs to be 108mm. Most spacers I've seen have smaller bores. You can usually tell just by looking if it's the right size if the hole for the lug nut almost touches the center bore hole. There is usually no more than ~1/8" (I'd say 1/16" is what I recall seeing) between the holes. See the spacer pic I posted from trailgear.com above.

HTH <img src="/forums/images/graemlins/kewl.gif" alt="" />