Back in the dark ages when Delco and AC were still made in America, AC 45 plugs were used in delivery trucks, taxicabs, and other inner city vehicles that did a lot of short trips, cold starts, and other uses that would foul the plugs. 43 or 44 plugs were "colder" and worked better on vehicles that got warmed up once and driven for longer distances. The extended tip plugs work better because the ceramic insulator sticks down into the flame front in the combustion chamber and is less prone to carbon fouling.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!