Greyhorn flat square 16mm natural. There are two different kinds of natural materials used in this product. Grey horn is actually horn from a water buffalo locally known as carabao in the Philippines. This color horn is not as readily available as the black horn therefore we do not carry as much variety as the other color horn. The other material used that has the same natural color as the grey horn is the caranail or the hoof of the water buffalo. Note that the horn is a byproduct of the food industry.