What Are Slotted Hex Nuts?
Slotted hex nuts—also called castle nuts—are hex nuts with slots cut into the top face. A cotter pin passes through a slot and the bolt’s cross-hole to create a positive mechanical lock that resists rotation in high-vibration or safety-critical assemblies.
Key Benefits of Slotted Hex Nuts
- Mechanical locking: Cotter pin through the slot prevents loosening without chemical threadlocker.
- Vibration resistance: Ideal for dynamic loads, impact, or cyclic motion.
- Serviceable design: Easy visual inspection; replace the cotter pin during maintenance.
- Material options: Zinc-plated steel for general use; 304/316 stainless for outdoor, marine, or corrosive environments; brass for non-sparking or decorative needs.
- Standards compliance: Available to common inch and metric specs for consistent fit and performance.
Common Applications
- Automotive suspensions, steering linkages, and brake hardware
- Heavy equipment and machinery assemblies
- Marine and coastal hardware
- Structural and industrial fabrications subject to vibration
- Aerospace, agricultural, and off-road equipment
How to Install a Slotted Hex Nut
- Torque the nut to the joint’s specified value.
- Advance (do not back off) the nut just enough to align a slot with the bolt’s cross-hole.
- Insert the cotter pin fully through the hole and slot.
- Bend the cotter pin legs around the nut to secure; trim excess if required.
Tip: Follow your drawing/standard for permissible additional rotation after reaching torque to achieve slot alignment.
Maintenance Tips
- Always replace cotter pins after removal; never reuse a bent or fatigued pin.
- Inspect slots and threads for damage or deformation before reassembly.
- Match materials to limit galvanic corrosion (e.g., stainless nut with stainless bolt in wet environments).
Materials & Finishes
- 304 Stainless Steel: General outdoor corrosion resistance.
- 316 Stainless Steel: Superior pitting resistance for marine/chloride exposure.
- Zinc-Plated Steel: Cost-effective protection for dry, indoor, or sheltered settings.
- Brass: Non-sparking, decorative, or low-magnetic applications.
Sizing & Standards
Available in inch and metric sizes in both coarse and fine thread pitches. Select the nut to match the bolt’s diameter and thread pitch; ensure the bolt has a cross-hole for the cotter pin and sufficient thread engagement (commonly at least one bolt-diameter, unless otherwise specified by your standard).