Spark Plug question

I'm running stock heat range plugs in my 1971 2000cc Capri. I'm concerned that they may be running a bit hot, especially since I found some little round metallic balls on the number 4 insulator.

Anybody know how the manufacturers numbers work. For example, the motor takes a Motorcraft 42 or Autolite 45 plug. Can I specify a different number to get a colder plug that still fits?

Yes, Joe.

Typically, the lower the number, the colder the range--Autolites for sure go that way.

Try one number down on the Autolite and see if they make it.

I'm sure you can Google this too.

Cheers.

Except for NGKs which have a higher number for a colder plug.