Gsf 400 bandit spark plugs issue

[epsavit]

hi everybody, i am new to this forum. i would like some technical help if possible regarding the spark plug types that fit in a Suzuki Bandit 400 93' model.
1) how do i distinguish what type of spark plug fits for my bike ? by what paramter ? (size ? make ? )
2) my previous mechanic used iridium spark plugs which felt like a lot of improvement comparing with my previous ones. i had to change mechanic and the new one says that this type of bike cant have iridium spark plugs fitted !!! which one is wrong and why ?
after search ont he internet i found ads about ngk 4218 spark plugs. they were advertized for bandit 400 too. i am confused as to what to do with my new mechanic. shall i accept his opinion and pay him for the service or i shall demand that he changes my spark plugs to the previous which were fine ?

thanks for your time

[pecha72]

I´d check it from the bike´s service data (service manual, service card or user manual - internet has all sorts of good & bad information!) and I would use the exact plug specified there. Using an Iridium type plug might be ok, if its the right one for your machine, but if the original is not Iridium type, then I dont believe there´d be a whole lot to gain.