In my desert riding days, always had this clampted to my frame somewhere in case I needed a spark plug out in the middle of nowhere. Sold the dirt bikes long ago and found this in one of my tool boxes and thought it would be nice to put two HD spark plugs in. The HD plugs threads are too small so was wondering whether someone makes a threaded insert that takes the threads from the old car size to the newer HD size?? See pics

 

They make thread adapters for almost every size I know of, as long as know your correct sizes, am sure can find one ..

 

But where do you find them?

 

After an hr of searching, found that the one I have has 14mm threads. The HD plugs are 12mm threads. So I need a 14mm male with a 12mm female thread in the center. I have found 18 to 14 and 12 to 14 but not 14 to 12.
Did find some that say 14 to 12 but they take a 12 into a 14, not what I want.