Hammer stones are known as the "original" percussion tool. Used by native Americans for thousands of years these hard stones are great for driving flakes like the Indians. This kit comes with 3 different sizes of stones. The smallest stone around 1.5in, Medium stone around 2.5-3in and Large stone around 4-5in. Each set of stones is different, the image shown is an example of what to expect. All the stones are fairly round and can be easily gripped.