And because the nut slots are spaced at 60-degree intervals, it may not be possible to tighten the nut precisely-it may have to be over- or under-tightened for the hole and a slot to align. This system does require that the hole be drilled in the correct place. Unless the cotter pin or safety wire shears (breaks), the nut remains in position. Once the nut is installed, a cotter pin or safety wire is inserted through opposing slots in the nut and the bolt's hole to prevent the nut from loosening. Slotted nuts are used with bolts or studs that have a hole drilled in their threaded section. Although effective, extra bolt length is needed to accommodate the additional nut, and installation time is increased because assembly involves two nuts that must be individually tightened. Said to be one of the first locking schemes, a thin "jam" nut is first installed and tightened, then the normal thick nut is installed and tightened against the jam nut. There are a variety of different free-running styles to choose from and, often, the application will dictate which is the most appropriate. However, that generally means there is substantial friction during assembly. Even after slight loosening, friction continues to resist further loosening. Prevailing torque types, however, are designed to create friction. Still, in some applications, that may not be a problem. Once initially loosened, however, they offer no further resistance to loosening, which is their main disadvantage. Regardless of the type, the objective is to increase the "break-loose" torque, which is the amount of torque required to loosen the fastener once it is installed.įree-running types often rely upon an additional component, such as a lock washer or jam nut. Basically, there are two types of locking fasteners: free-running and prevailing torque. In this section we'll look at some of the more common non-permanent locking schemes (an example of permanent locking uses a chemical reaction to form an adhesive that bonds with the mating threads). A locking fastener is designed to resist loosening and can be externally threaded, such as a screw, or internally threaded, like a nut.
In these situations, a "locking" fastener may be required. Threaded fasteners (bolts, screws, etc.) can loosen when exposed to shock, vibration and other dynamic forces.
#Whiz nut series#
Fastener Tech Data | Understanding Series Introduction