AC plugs have heat ranges that go up as the number increases. A 44 is hotter than a 43, and a 45 is hotter than a 44. 43's are supposedly for highway driving, 44's are multi-purpose, and 45's are for short-trip or other limited duty use. The "C" prefix was for a "commercial" plug, used for delivery trucks, taxicabs, and other fleet-type vehicles. They have larger center electrodes, and heavier ground tabs, and they last forever, even under severe conditions. If your C44's are clean and properly gapped, they're the best possible plug for your engine. They're also almost impossible to find these days. We used to use them in the round track race cars, and they would outlast regular plugs about 3 to 1. Hang onto them!
Jerry
