The numbers refer to approximate drying times in hours (at 68F): DRY FLEX® 16 is ideal for larger projects where time is not a factor; DRY FLEX® 4 is suitable for small and large repairs that need to be completed within a day; DRY FLEX® 1 is suitable for fast, small repairs from 3/16” to 3/8” (or 5 – 10 mm) in depth, such as emergency response maintenance. Further details can be found on the products page.