These Survey Spikes are made of hardened steel and have a dimpled or square gear head, which is great for establishing a point. All spikes are four inches long by 1/2 stem at the head tapering down to 1/4". The spike is perfect for driving into a variety of surfaces, such as asphalt, concrete, stone and hard soils. Can be used as corner, offset angles, and permanent markers. They come in boxes of 50 or 100 count.