5/16"-18 Socket Head Cap Screws

5/16-18 Socket Head Cap Screws in all available lengths, grades, materials, and finishes. This collection covers every 5/16-18 option in stock — use the filters to narrow by length, grade, material, and finish.

5/16-18 Thread Specifications

• Nominal diameter: 0.3125"
• Threads per inch: 18
• Tap drill (75% thread): F (0.257")
• Clearance hole (close fit): 21/64" (0.328")
• Clearance hole (free fit): 11/32" (0.344")

To thread a 5/16-18 hole, drill with a F (0.257") tap drill for a standard 75% thread. For a clearance hole that the 5/16-18 screw passes through, use 21/64" (0.328") for a close fit or 11/32" (0.344") for a free fit. Pair with a matching 5/16-18 nut or tapped hole.

Orders before 12 PM ET ship same day.