14 mm/10 mm plugs?

Posted by Oldrookie On 2018/11/10 21:34:47

I recently purchased a 1938 1601-D and all of the information indicates that 10 mm spark plugs are used with this model. The plugs that are in the vehicle are 14 mm. Were certain 38's equipped with heads that were tapped for 14 mm plugs, or is it more likely that the head was swapped with a different model?
Any idea as to what the right plug would be to use. There are currently Champion UJ 12Y plugs in the car.
Thanks for any info you may be able to supply.