Dixon Lumber Crayons last up to 10 times longer than ordinary molded wax crayons. Fade-proof, water-proof, smear-proof, these crayons won't melt in direct sunlight. They will work on wet (green) lumber or dry wood, metal, concrete and most other surfaces. Each crayon is individually UPC coded and hex shaped (4-1/2 x 1/2 inches) to fit lumber crayon holders.