These hooks are perfect for concrete or masonry walls. Not for use on hollow or soft wall surfaces. Perfect for hanging picture frames on solid walls or on wooden furniture, also suitable for other small gadgets, cloth or hats. Great for hanging picture frame, clocks or decorations on wooden wall, hard wall surface. Easy to use, just hammer pins straight in. Easy to remove and will not leave a big mark. Please allow 1-2mm error due to manual measurment.