A nut is a standard fastener with internal thread. It works together with bolts or studs to form a threaded pair. Many engineers treat nuts as simple locking parts, while ignoring the anti-loosening mechanism and strength matching rules. Improper selection will lead to connection failure under vibration or temperature cycling load.
Main Functions of Nuts
Engage with external threads of bolts, generate preload force after torque application and clamp workpieces;
Flange nuts have integrated flange face to enlarge contact area, reduce pressure and protect soft materials such as aluminum sheets;
Lock nuts increase friction between threads to resist vibration and prevent loosening;
Dome cap nuts cover exposed threads for corrosion protection and better appearance.
Common Nut Types & Features
Hex Nut: General industrial type (DIN934, GB/T 6170). Stable force for wrench operation. Thin hex nuts are used where space is limited and not for primary load;
Flange Nut: Integrated flange, no separate washer required for faster assembly;
Nylon Insert Lock Nut: Built-in nylon ring grips the bolt shank after tightening, good vibration resistance and reusable;
Castle Nut: Matched with cotter pin for mechanical locking, widely used in vehicles and construction machinery with high safety requirements;
Wing Nut: Hand-tightened without tools for frequent light-duty disassembly;
Weld Nut: Welded on sheet metal to provide stable internal thread.
Standards & Property Classes
Main standards: GB/T 6170, GB/T 6172, DIN934, ISO4032. Common property classes: 5, 8, 10, 12. Important rule: High-strength bolts must be matched with nuts of equivalent class. Lower-class nuts are prone to thread stripping under high preload.
Material & Surface Treatment
Material: Carbon steel, 304(A2) stainless steel, 316(A4) stainless steel, brass, alloy steel;
Finish: Zinc plating, black oxide, Dacromet, hot-dip galvanizing, mirror polishing. Tip: 316 stainless steel or Dacromet coating is recommended for humid and marine corrosive environments.
Engineering Selection Guide
Thread size and pitch must fully match the bolt; metric and imperial threads cannot be mixed;
Nylon lock nuts or castle nut + cotter pin are preferred for continuous vibration conditions;
Flange nuts are recommended for soft sheet metal to avoid crushing;
Nylon lock nuts are not suitable for high-temperature service, as high heat will damage the nylon insert.