I have used the Monark plugs. So far I've replaced two of them after about 10k. I had no choice at the time. I need to use a conversion plug. I have a 77 engine(loop type plug) in a 80 car(pin type). The conversion plug has the big body(21mm) of the loop type plug with a pin type element. I had a few of the Bosch plugs for spares. I was told Bosch didn't make them anymore. andy