Single-thread-engaging nuts are formed by stamping a thread-engaging impression in a flat piece of metal. They are used for lighter-duty applications than multiple-thread nuts of the same size. These fasteners reduce costs when used in place of ordinary fasteners. They eliminate several assembly steps and reduce the required number of parts.
Unlike multiple-thread nuts, single-thread types do not require a large amount of torque. Their holding power and resistance to vibration loosening depend solely on spring action.
Because only one screw thread is engaged at a time, the prongs cannot "freeze." This can be important in applications where fasteners are exposed to corrosive conditions, and ease of removal is a factor.
Single-thread-engaging nuts will withstand greater tensile loads when screw holes have minimum clearance. (This does not apply to the self-retaining type where part of the nut snaps into the clearance hole.)
The proper machine screw length to be used with single-thread nuts is determined by the general practice used with conventional threaded nuts: Allow one thread to protrude beyond the thread-engaging element of the fastener. However, sheet-metal screws that taper at the end should protrude a minimum of three threads beyond the thread-engaging element to assure engagement on the full screw root diameter.
It is possible to design this fastening device in almost any physical shape. The helically formed prong and truncated-cone types are best used as nuts into which the screw is driven. Spirally formed thread-engaging elements can be stamped into hexagonally formed nuts, acorn locknuts, washer nuts, and wing nuts. Single-thread-engaging spring nuts can also be furnished with preassembled clinched screws.
Because of their spring lock and resistance to vibration loosening, single-thread nuts eliminate the need for lockwashers. In addition, their design versatility makes them valuable in blind fastening locations and multiple fastening locations.