Found this explanation on zinc wicks on Taylored Concepts website: This wick has a cotton outer braid surrounding a thin filament of zinc. Zinc core wicks product the coolest flame and offer the most rigidity of all cored wicks, providing support during pouring and burning. What do the wick numbers mean? The first set of numbers is the thickness of the wick, the larger the number, the thicker the wick. The second set of numbers is the speed at which the string goes through the wicking machine gear, the faster it goes through, the tighter the wick and the slower the burn. The third set of numbers is the code for the temperature of the Wax as the wick goes through the various gears.