These are the most common types of rounded-head screws, Phillip Head Screws, Nut Head Screws and perfect for applications such as watches, bracelets, bezels, necklace, findings, earrings,. Machine threads are used in a pre-tapped hole or with a nut. These are 3D models , They are STL files and its ready for 3D printing, Please look at the pictures for more information.