For attaching friction stays with countersunk holes to steel reinforced PVCu frames. Stainless steel should be used where there is a corrosive environment. Thread Dia. mm: 3.9 Length mm: 25 Head Type: Shallow Pan Countersunk Recess Type: Phillips Thread Type: Self-Tapping Point Type: Self-Drilling Material: Martensitic Stainless Steel (410)Size 3.9x25 1000Pcs Timco Window Screws Friction Stay Pan Self-Tapping Thread in Silver