Push On Fasteners Information
Push on fasteners, also known as push on retainers or push in fasteners, are hardware components that allow components to be quickly and securely assembled to a smooth shaft. A push on fastener is constructed with radial fingers or teeth that are formed at an angle perpendicular to the shaft. This angle allows the fastener to slide onto the shaft in one direction while resisting motion in the reverse direction, providing sliding resistance to the assembly.
This attachment mechanism is similar in principle to the barbs on fish hooks or porcupine quills. During assembly, a push on fastener slides quickly on the shaft and provides instant holding power. Other names for push on retainers used throughout the world are push on fix, push ons, hub nuts, quick lock washer, and axle washer.
There are several types of push on fastener.
- Push on nuts / push nuts – These are the most common type of push on fastener. Other common names are external fixing washer, push on retainer, and Starlock® washer. It is important that the shaft material is softer than the push nut.
- Push on hat retainers – This type has a cap that covers the end of the rod or shaft providing protective and aesthetic benefits. Also known as cap nut, washer cap push nut, and hammer cap push nut.
- Speed nut – A speed nut slides quickly onto the shaft and is then locked with a radial motion applied to a self-threading feature.
- Push-on bolt retainer – Slips onto bolts and screws to hold them in position in panel or other assemblies while a traditional nut is installed.
Many push on fasteners are made from spring steel. Other materials that are used to better suit operating conditions include stainless steel, aluminum, plastic, and bronze. Typical coatings and finishes found on push on retainers can be zinc plating, passivation, and enameling.
The rod or shaft design is an important consideration. A tight shaft diameter tolerance (typically .002 for small shafts and .004 for larger shafts) ensures that requisite holding force will be supplied by the push nut. The rod material must have adequate hardness but not exceed a value that prevents the locking teeth to dig in (such as 78 on Rockwell 30T scale.) Also, shaft cutoffs need to be rounded or chamfered to allow quick and easy mounting of the push retainer.
Push on fasteners can provide component cost and assembly time savings in a well-suited application. In addition to providing a finished attachment function, a retaining fastener can be used to temporarily hold an assembly together before and while a higher strength fastening mechanism, such a locknut, is attached. Complex and multi-staged assemblies can benefit when there is physical transit between assembly stations. Push on fasteners are used in a wide variety of applications including automotive, medical, and consumer products, such as furniture or toy assemblies that contain shafts and axles.