Hi all just wondering i am trying to change the spark plugs on my vauxhall astra 1.6 club 8 Valves(year 2001); i went to my local Halfords and found out that there are two Bosch Spark plugs sets that fit my model with two different electrode gap distances ( i think 16 and 21 mm - if i am not wrong); what would be suitable and what is the difference between them many thanks in advance for your help Carlo