Slotted Hex Nuts

Slotted hex nuts are standard hex nuts with slots cut across the top, allowing a cotter pin to pass through the slots and a cross-drilled bolt to mechanically lock the nut. They provide positive, tamper-evident retention where vibration could loosen a plain nut. Common on axles, machinery, and safety-critical joints, we stock slotted hex nuts across grades and materials.

How Slotted Hex Nuts Work

The nut is tightened, then aligned so its slots line up with a hole drilled through the bolt. A cotter pin is inserted through the slots and bolt hole and bent open, mechanically preventing the nut from backing off. Unlike friction locking, this is a positive lock that cannot loosen — essential for wheel bearings, steering, and other safety joints.

Slotted Hex vs. Castle Nuts

Slotted hex nuts have slots cut into a standard-height hex nut. Castle nuts have a raised circular crown above the slots (the castellations), giving more pin clearance and the classic battlement look. Both serve the same cotter-pin locking function; choose by clearance needs and specification.

Grades and Materials

Grade 2, 5, and 8 steel for general to high-strength use, typically zinc plated. 18-8 and 316 stainless for corrosion resistance. Match the nut grade to the bolt.

Dimensional Standards

Slotted hex nuts conform to ASME B18.2.2, sized by thread with standard slot dimensions for cotter pins.

Selecting the Right Slotted Hex Nut

Match thread size, pitch, and grade to the bolt, and ensure the bolt is cross-drilled for the cotter pin. Choose material for the environment. After tightening to spec, align a slot with the bolt hole (advance slightly to the next slot if needed), insert a new cotter pin, and bend the legs. Always use a fresh cotter pin on reassembly.

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