Short, thick outgrowths that allow prokaryotes to attach to surfaces or each other are called

Short, thick outgrowths that allow prokaryotes to attach to surfaces or each other are called pili.
Pili are small hair-like structures that enable some bacteria to attach and adhere easily to the cell surface. They are shorter and more numerous than bacterial flagella and are composed of a protein called pilin. There are two types of pili:
1. Sex pili-for the conjugation (the transfer of genetic material between bacteria)
2. Common pili-for the solid surface attachment.