A mason's most delicate tool is the level, but it often gets rough treatment on the jobsite. CARING FOR YOUR LEVEL Caring for your level just takes a little forethought. Oil wood levels with a rag and raw linseed oil at least once a month. The oil helps keep mortar from sticking to the level. Most importantly, hang a level from a nail when it's not in use. ONLY BUY LEVELS WITH ANTIWARPAGE GUARANTEES Both aluminum and wood levels can warp, but some manufacturers have guarantees against warping. Be sure the level you buy has a written warranty attached to it. Most high-quality levels are made of wood. They give more consistent readings than aluminum levels, which can give different readings in different temperatures. Rubber cushions or soft plastic at the ends of the level offer good protection. To keep wood levels true, they may have a metal I-beam running through the middle or tongue-and-groove construction. WOOD LEVELS SHOULD BE BOUND Because brick is abrasive, levels with no metal strips of binding around their edges often wear down, becoming less accurate over time. Binding protects the edges. THE VIAL IS IMPORTANT TOO A level should have two crown (curved) vials in each window. Make sure the bubble fills the distance between the lines on the vial exactly. A crown vial holds the bubble in place better than a barrel (straight) vial. Choose Pyrex glass, too, because it's stronger than plain glass.