Sheets & Articles
CHALLENGE OF FASTENING
WHERE ONLY ONE SIDE IS ACCESSIBLE
Most fasteners designed
to provide permanent load-bearing threads in thin materials require
both sides of a workpiece to be accessible during installation and final
component assembly. For those instances where there is access from only
one side, so-called "blind" applications, threaded rivet nuts (also
known as blind threaded rivets, blind rivet nuts, and threaded inserts)
can provide a solution. And, with inaccessibility no longer an obstacle,
threaded rivet nuts are ideally suited (where other permanently installed
threaded hardware is not) for tubing, extrusion, and other similar types
Threaded rivet nuts
are made from aluminum, brass, steel, or stainless steel and are designed
to be used instead of tapped holes, weld nuts, rivets, and self-drilling
or tapping screws. Installed from the accessible "front" side of a workpiece,
these rivet nuts will provide strong permanent metal threads in metal
or plastic sheets as thin as .020"/0.50mm, which can promote thinner
and lighter product designs.
nuts further eliminate any need for additional hardware beyond a mating
screw to complete final component assembly. This can save time and money
during production, due to fewer parts and assembly steps.
In attachment applications
where components will need to be taken apart for service, threaded rivet
nuts also will prove more practical than rivets or adhesives, which
make disassembly impossible.
Unlike weld nuts
or press-in type nuts, threaded rivet nuts can be installed anywhere
in a shop without requiring product-dedicated assembly locations and
they can be installed anywhere and anytime in the field during end-product
maintenance or repair. Rivet nuts can be installed even after product
finish is applied, because the compatible lightweight, portable hand-held
installation tool will not damage the finish.
In general, the
installation procedure into metal or plastic sheets of any hardness
begins by threading a rivet nut onto the tip (pull-up stud) of the installation
tool and inserting the fastener into a drilled or punched hole. When
the tool is activated, the pull-up stud retracts and bulges the unthreaded
portion of the rivet nut shank against the reverse side of the sheet
to lock the rivet nut permanently and securely in place. The tool is
then simply reversed to remove. A mating screw completes the assembly.
Some typical real-world
applications for these rivet nuts include attaching aircraft seat trays,
automobile mirrors and lights, luggage rack rails for vehicle roofs,
automotive radiators, trunk "spoilers," ABS module mounting on vehicle
dash panels, electronics cabinetry hardware, and appliance handles and
hinges, as well as closed-structure sections with minimum backside clearance
such as roll forms, tubing, and extrusions.
Two Product Groups
Threaded rivet nuts
can be classified in two basic groups: standard and heavy-duty. Standard
rivet nuts will satisfy most blind applications where permanently installed
threads are required. Heavy-duty rivet nuts (featuring heavy-duty heads)
are engineered for the more demanding, high-performance applications.
fasteners are available in unified and metric thread sizes from #6-32
to 1/2"-16 and M4 though M10; heavy-duty fastener thread sizes typically
range from #4-40 through 1/2"-13 and M3 through M12. Both groups of
rivet nuts are designed (and can be customized) with a variety of head
and body configurations to meet specified parameters of a given application.
A variety of fastener
types within both general groups have been developed, based on common
industry usage. The standard family of threaded rivet nuts includes
these five designs:
Half-Hex Shank Low-Profile Head:
Features a hex body design and improved torque resistance.
Rib-Wall Low-Profile Head:
Features a large diameter, low-profile head, and knurled shank to offer
high all-around strength.
head profile compared with the low-profile type allowing near-flush
installations with no need for special hole preparations such as countersinking
Low-Profile Head: Features a low-profile head design and achieves flush
installations with no need for countersink drilling or dimpling of the
360 Degree Swaging
Works in any material thickness over .029"/0.76mm including blind hole
and exhibits high resistance to torque out. Nearly flush when installed
with minimal backside protrusion for restricted space applications.
The heavy-duty family
of threaded rivet nuts includes countersunk and flat-head fasteners.
offer the advantages of enhancing end-product appearance and enabling
sheet-on-sheet attachment, since the countersinking feature allows the
fastener to be installed flush with the surface of a sheet. These fasteners
are available with rib or key features for high-torque applications.
Flat-head types, which are also designed for high-load applications,
are offered with open- or closed-end designs and with or without ribs.
The technology behind
the tooling to install threaded rivet nuts has been engineered to work
hand-in-hand with standard or heavy-duty fastener design and function.
Dedicated tooling has been developed for both groups of rivet nuts.
tooling for standard rivet nuts utilizes "spin/spin" technology. In
these installations, the fastener is fixed to the tool mandrel about
a quarter of a turn. After the fastener is placed into the mounting
hole, the tool is engaged. Its spinning action draws in the fastener,
collapsing the fastener wall. When the tool stalls and the fastener
is collapsed, the tool can be disengaged and reversed so that it spins
out of the installed fastener. Installation is then complete.
installation tooling for heavy-duty rivet nuts utilizes "spin/pull"
technology. In these installations, the fastener is fixed to the tool
mandrel until the rivet nut is snug on the anvil. After the fastener
is placed into the mounting hole, the tool is engaged, powered by an
hydraulic cylinder. When the fastener is installed, the tool is reversed
so that it spins out of the installed fastener. Installation is then
With proper tooling
and quality parts, users can achieve reliable fastener-installation
rates up to 500 rivet nuts per hour (hand tools are available for low-volume
applications). In the process, assembly (and disassembly) benefits offered
by threaded hardware can be realized in "blind" attachment applications
that otherwise would not be possible.