Back in the 1960's, Volkswagen bugs had rigid spark plug caps with a big circular rubber water shield. You had to unscrew the tip of the spark plug to expose the threads on the bare tip and then the tip would fit in between the gripper prongs of the cap. I noticed the similarity to the plug caps on my '14 Cal Touring bike. Have not gotten a VW spark plug cap to compare to the one in my bike. Not to send anyone on a wild Goose chase, but I plan on looking into it. And those VW parts were Bosch.You do know that NGK pulled out of the spark plug cap business? Yes?
They discontinued the entire line. If you go to their website, many are showing No Longer Available.
As far as I have discovered, only remaining stock is being sold. No back orders will be filled.