The end that goes into the spark plug cap is threaded inside the end of the spark plug end. While the one I need has the threaded end that stucks outside the end of the spark plug (like a screw).
I think someone has changed the boot before.
Any MC shop, possibly even a small engine shop should have the style you should use.
I get mine at local MC shops or scooter shops for $2.99-4.50...approx...