Rhino Rulers Folding Modular Brick Spacing Ruler 6' Length - 55120 Model 55120 is for laying bricks in conjunction with concrete blocks as backing Made of polyamide reinforced with 30% fiberglass; Lasts 3x longer than wooden rulers Waterproof; Will not warp or swell like wooden rulers; Wear resistant and maintenance free Deeply embossed scales won't wear away under harsh working conditions Flexible and scratch resistant with 90 positive stop joints