One of my plugs becamed fouled enough and gave up on me today. Fortunately I was within minutes of an auto department store, and I found a set of Bosch Super-4 plugs to replace my OEM single electrode ones. Supposedly, the spark can take one of eight paths, thereby reducing the possibility of mis-firing.
Anyway... just thought I'd share with those of you in the market for new plugs. Fits all Volvos (amongst others) models 240 through 940, or all 4 cylinder motors from 1984~1995. (B18, B200, B230)(I read my old plugs - and I suspect they prematurely failed because I had starter trouble and had to crank many times before the gears finally "caught" on. Either that or, it's related to the knocking sound I sometimes got while under load and hot weather. I'm back to using Premium grade now.)