Markal 200 Lumber Crayon Economical Wax Based Marker, 1/2" Hex, 4-5/8" Length, Black (Pack of 12) Known as layout chalk or "keel" Lead-free; economical Dimensions: 1/2" hex by 4-5/8" long Use on lumber, concrete, metal, plastic, rubber, paper, cardboard, and ceramics Standard 1/2" hex shape fits the #109 peterson holder, #106 holder and #108 holder