Some year Triumphs specified N12's; later versions had N9s. But most drivers know that if you need a hotter plug the N12s will work an any year TR6. All of the high-priced super plugs are just a waste of money if you are driving a classic low-compression classic British sports car. Owners know whether they need a hotter or cooler plug - the tables only recognize what was originally in the car, but mechanics for years have specified N12s when the cooler plugs were not keeping the cylinders clean (particularly in cars that don't get high-speed long-distance driving).Like oils and other products, though, there are many different opinions on the best plugs for a car. These and the N9s are the OEM choice, and in my experience work just great. And the price is great, too.Some owners have reported difficulty in obtaining these #38s; I don't know why that is, but stocking up is a good idea before they become "unobtanium".