plug numbers?

can anyone tell me what the part number is on a 1 step colder plug? the number ive got is azfs32fef4? is that correct? and should i go 1 or 2 steps colder with a 75shot?

1 step for ever 50hp, thats not the number i rember. i have 22c's...they added another letter on the end after c though now, may be g.