[Rob09msport]

Alot of confusion on plugs here. N20 is 97506 plugs and s55 and n55 are no different spec wise just one is an m variant and they sometimes are actually cheaper for the s55 but the insulators are known to crack. BMW used bosch 4 electrode on n54 ,then went to ngk single tip and then went to bosch single tip on the newer engines so depending on yr you could lookup and find a ngk or bosch. It's better to go off model which I believe are ZMR5TPP330 and zr5tpp33s. The only real flop plug I believe was the gtr plugs but you can decode the plug by model number to see thread size and length ,electrode type,heat range etc. When you do this you realize how simple it really is.