Markal 500 Lumber Crayon Clay Based Marker, 1/2" Hex, 4-5/8" Length, Red (Pack of 12) Known as layout chalk or "keel" Clay based formula provides longer marking mileage; lead-free Dimensions: 1/2" hex by 4-5/8" long Use on lumber, concrete, metal, plastic, rubber, paper, cardboard, and ceramics Makes weather-resistant, water-resistant marks