Ideal for marking straight lines on flat surfaces between two points using a chalk line, perfect for flooring, dry walling and brick laying applications. The IRWIN STRAIT-LINE blue marking chalk has been designed to leave a permeant mark on a surface both indoors and outdoors for 1 week. The innovative flip-top cap that keeps the chalk in the bottle where you want it. The flip-top cap seals the chalk in an airtight chamber, keeping out moisture and reducing the risk of clumping. The IRWIN Blue Marking Chalk has been designed to be accurate, making it an essential tool in any DIYer's toolbox.