Flat Head has a countersunk flat head with a cone-shaped bearing surface. Used in applications where the protrusion of the fastener about the bearing surface is unacceptable. Machine threads are used in pre-tapped hole or with a nut. Zinc is a popular and economical plating and is a good choice for interior applications when working with acidic woods like red/white oak, or when the screw will be countersunk and plugged.