Hex nuts are a popular fastener. They are hexagon-shaped with slots on the top that allow a cotter pin or split pin to be inserted. These nut styles are thicker than the average nut and are usually used on large bolts and bolt heads. They are available in diameters ranging from 1/4-1/2 inches to four inches.
They are similar to castle nuts, but have slots cut into the top. These slots allow for the insertion of a cotter pin or safety wire. They are also commonly used in automotive applications and machinery. These nut styles also feature a deformed top that prevents them from being unscrewed and thus create a locking effect.
The nominal size of these nuts is 5/8 inches, but larger sizes are available. The larger sizes are double chamfered with a washer faced bearing surface. They are manufactured to meet the specifications of ASTM F 594 and ASTM F 467. They are generally used on large bolts with a 60-degree thread angle.
Slotted nuts are similar to castle nuts and are used in applications where vibration may loosen the assembly. Many manufacturers prefer these over castle nuts because they eliminate the need for lock washers and cotter pins. They can also be interchanged with each other.jinduhardware.com