Thanks to Chris Forbes at Knovel Corporation for explaining what the 40 in WD-40 means. He says, “It took them 40 attempts to get the water displacing formula worked out”. Chris also says that the name came from “Water Displacement perfected on the 40th try”. They obviously did a really good job because the original secret formula for WD-40 is still in use after fifty years. I always have a few cans around the shop.