Which fastener has a drilled head for safety wire?

Which fastener has a drilled head for safety wire?

• A. Clevis Bolt
• B. Eye Bolt
• C. Fillister
• D. Plain Washer

Answer: (C)

Safety wiring is used to keep fasteners from loosening in vibration, so you pass a wire through a hole in the fastener head and twist it to a fixed point. The fillister head screw is the one designed to be drilled for that purpose, providing a head that can accommodate a small hole without compromising the shank. The other options don’t typically feature a drilled head for safety wire—eye bolts and clevis bolts have different primary forms (a loop or clevis feature), and plain washers have no head at all. So, the fillister head screw is the fastener chosen for safety wiring.

Safety wiring is used to keep fasteners from loosening in vibration, so you pass a wire through a hole in the fastener head and twist it to a fixed point. The fillister head screw is the one designed to be drilled for that purpose, providing a head that can accommodate a small hole without compromising the shank. The other options don’t typically feature a drilled head for safety wire—eye bolts and clevis bolts have different primary forms (a loop or clevis feature), and plain washers have no head at all. So, the fillister head screw is the fastener chosen for safety wiring.