i use them there 4 prongs things take them out every now and then just to stop thread lock had them in now for 12 months should be ok for another 12 months pricey but good
As Craig says get a set of W8AC in Bosch,you will find less problems,over the years we have seen lots of problems with other plugs such as the thread protruding into the combustion chamber,getting a build up of carbon and bringing the thread with it on removal, wrong heat range causing fouling or burning the electrodes.