3.5-inch HDD Tray Mounting Screws - Set of 40 These screws are specifically designed for NAS devices from manufacturers such as QNAP, I-O DATA, Synology, and ASUSTOR. They are ultra-low profile countersunk screws designed to prevent the HDD tray screws from catching on the inner rails of the NAS. Screw Type: Inch screw #6-32 (for 3.5-inch HDDs) Screw Length: 5.9mm (including screw head)