Autolite indicates the heat range with the last digit of the part number. For example, 3923 has a heat range of 3. The higher the number, the hotter the plug. The lower the number, the colder the plug.
For instance, starting with part # 24 (heat range 4), if you want a colder plug you would use part # 23 (heat range 3), for a hotter plug you would use part # 25 (heat range 5).
Once you have decided on a number, test to see if it exists by typing it into the search box. If it exists, you can add the part to your cart. For additional assistance contact our tech team at 888-800-9629.