![TIME-SERT_thread_insert](https://upload.wikimedia.org/wikipedia/commons/c/ce/TIME-SERT_thread_insert.gif)
A threaded insert, also known as a threaded bushing, is a
fastener
A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or disman ...
element that is inserted into an object to add a
threaded hole. They may be used to repair a stripped threaded hole, provide a durable threaded hole in a soft material, place a thread on a material too thin to accept it,
mold
A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...
or
cast
Cast may refer to:
Music
* Cast (band), an English alternative rock band
* Cast (Mexican band), a progressive Mexican rock band
* The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis
* ''Cast'', a 2012 album by Trespassers William
...
threads into a work piece thereby eliminating a machining operation, or simplify changeover from
unified to
metric threads or vice versa.
Types
Thread inserts come in many varieties, depending on the application. Threaded inserts for plastics are used in plastic materials and applied with thermal insertion or ultrasonic welding machines.
Manufacturers of
ready-to-assemble furniture
Ready-to-assemble furniture (RTA), also known as knock-down furniture (KD), flat pack furniture, or kit furniture, is a form of furniture that requires customer assembly. The separate components are packed for sale in cartons which also contain ...
often ship the parts with threaded inserts and other kinds of
knock-down fastener {{sources needed, date=June 2021
Knock-down fasteners are a class of fasteners designed to allow for repeated assembly and disassembly. They are often used in flat pack furniture, which is typified by items such as book cases and wall units that c ...
s pre-installed.
People who use
sheet metal
Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Sheet metal is one of the fundamental forms used in metalworking, and it can be cut and bent into a variety of shapes.
Thicknesses can vary significantly; ex ...
or
sandwich panel
A sandwich panel is any structure made of three layers: a low-density core ( PIR, mineral wool, XPS), and a thin skin-layer bonded to each side. Sandwich panels are used in applications where a combination of high structural rigidity and low ...
or honeycomb
sandwich-structured composite often install threaded inserts to spread shear, tension, and torque loads over a larger area of the material.
Captive nut
Captive nuts come in two basic styles. One type, the
cage nut
A cage nut or caged nut (also called a captive or clip nut) consists of a (usually square) nut in a spring steel cage which wraps around the nut. The cage has two wings that when compressed allow the cage to be inserted into the square holes, fo ...
or
clip-on nut A clip-on nut, also known as a sheet metal nut or a speed nut (but this is ambiguous, see speed nut), is a type of nut designed to be clipped to sheet metal. It is a type of captive nut commonly made as a cage nut.
Types
They come in many forms ...
is a conventional nut held captive by a sheet metal carrier that clips onto the part to be connected. These are generally used to attach screws to sheet metal parts too thin to be threaded, and
they can generally be attached, removed and reused with simple hand tools.
The second type of captive nut is a threaded insert. These are either pressed into holes in the material to be joined or moulded in. In either case, part of the insert is generally
knurled
Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is rolled into the material.
Etymology
The terms ''knurl'' and ''knurled'' are from an earlier ''knur'' ‘knot in wo ...
to get a good grip on the material supporting the insert. One variant, the
swage nut, has a knurled portion that
swages the sides of a soft metal hole to more tightly grip the nut.
Press fit
An interference fit, also known as a pressed fit or friction fit is a form of fastening between two ''tight'' fitting mating parts that produces a joint which is held together by friction after the parts are pushed together.
Depending on the am ...
and swaged captive nuts are used in panels that are too thin to be threaded or in soft materials that are too weak to be threaded. They are installed by pressing them in with an
arbor press
An arbor press is a small hand-operated press. It is typically used to perform smaller jobs, such as staking, riveting, installing, configuring and removing bearings and other press fit work. Punches, inserters, or other tools/dies may be add ...
.
Threaded inserts are commonly used in plastic casings, housing, and parts to create a metal thread (typically: brass or stainless steel) to allow for screws to be used in the assembly of many consumer electronics and consumer products. These may be cast in place in
injection molded
Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...
parts or they may be added by thermal insertion. In the latter, the insert is heated and then pressed into a hollow in the plastic part. The heat causes local melting in the plastic. Ultrasonic Insertion is the process used to apply vibration and pressure to install the threaded insert into a molded hollow boss (hole) of a plastic part. The ultrasonic vibrations melt the
thermoplastic
A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains associate ...
material where the metal insert is in contact, and pressure is applied to press it into position. The material typically reforms around the knurled body of the threaded insert to ensure a good retention.
Externally-threaded inserts
![Taplok Insert](https://upload.wikimedia.org/wikipedia/commons/e/eb/Taplok_Insert.jpg)
Externally threaded inserts have threads on the outside and inside of the insert. The insert is threaded into a pre-tapped hole, or some inserts tap their own threads in a drilled or molded hole. It is then anchored by various means, such as a nylon locking element. Inserts that are anchored via
Loctite are more commonly known by the trademarked name ''E-Z Lok''. A thin walled solid bushing insert by the trademarked name ''TIME-SERT'' is locked in by rolling the bottom few internal thread into the base material with a special install driver which will permanently lock the insert in place. Key locking inserts, more commonly known by the trademarked name ''Keenserts'', use keys that are hammered into grooves through the threads, permanently locking the insert.
[McMaster-Carr, p]
3204
Inserts that are self-tapping and lock via friction are more commonly known by the trademarked names Tap-lok or Speedserts.
Helical insert
![Helicoil plus](https://upload.wikimedia.org/wikipedia/commons/a/af/Helicoil_plus.jpg)
A helical insert is an insert made of coiled wire. The helically formed coils of diamond shaped
stainless steel or
phosphor bronze
Phosphor bronze is a member of the family of copper alloys. It is composed of copper that is alloyed with 0.5–11% of tin and 0.01–0.35% phosphorus, and may contain other elements to confer specific properties (e.g. lead at 0.5–3.0% to form ...
wire screw into a threaded hole to form a mating internal thread for a screw or stud. These inserts provide a convenient means of repairing stripped-out threads and are also used to provide stronger threads in soft materials such as aluminium, zinc die castings, wood, magnesium etc. than can be obtained by direct tapping of the base metal involved. Another common generic name is screw thread insert (STI), although many users call them all by a prominent brand name, the
registered trademark
The registered trademark symbol, , is a typographic symbol that provides notice that the preceding word or symbol is a trademark or service mark that has been registered with a national trademark office. A trademark is a symbol, word, or wor ...
Heli-Coil. Applications include engine cylinder head repair after unintentional over-torquing or cross-threading of spark plugs strips the thread of the socket. Kits with matched tap and coil exist for this. The straight radial piece in the photo is the driver tang which is used as a key to grip with pliers for driving the coil into place and is discarded after installation.
Mold-in inserts
Mold-in inserts are internally threaded and have a specially shaped outer diameter to anchor the insert in plastic. The insert is placed in the mold of an
injection molded
Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...
part beforehand. The mold is then closed and filled with the plastic filling in around the insert. These inserts can also be heated and pressed into pre-made
thermoplastic
A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains associate ...
s.
[McMaster-Carr, p]
3209
For softer more pliable plastics, hexagonal or square inserts with deep and wide grooves allow the plastic to flow and adhere. The process allows large product manufacture i.e. fuel tanks, boats etc., so the torque inserts may be of large thread sizes.
Press fit inserts
![Press-in Insert](https://upload.wikimedia.org/wikipedia/commons/3/31/Press-in_Insert.png)
Press fit inserts are internally threaded and have a knurled outer diameter. They are pressed into a plain hole with an arbor press.
Potted inserts
An insert that is potted-in refers to the application of epoxy to fix it to a panel, such as a honeycomb sandwich panel, which are often used in commercial aircraft.
Strength factor for threaded inserts
''Resistance'' is the key strength factor in case of inserts, pull-out & torque-out are the two parameters to judge inserts.
* Pull-out: the force required to pull the insert out of the parent material.
* Torque-out: the amount of torque required to turn the fastener without inducing any clamp load on the fastener.
Knurling
Knurling is the metalworking which is done on the outer side of the component. In case of Brass Insert, knurling plays an important role in increasing pull-out & torque-out resistance. Types of knurling and its benefit are as follows:
* Straight knurls: Greatest torque resistance
* Diagonal or helical knurls: Balance resistance in both direction
* Hexagonal or diamond knurl: Most common and offers resistance in all direction
Installation methods
For industrial purposes, following installation methods are the standards:
* Thermal insertion
* Injection molding
* Manual pressing
See also
*
Insert nut An insert nut provides a threaded socket for a wooden workpiece, similar to a wall anchor. Insert nuts are inserted into a pre-drilled hole by one of two means: screw in and hammer in. In both cases, the external protrusions bite into the wood, prev ...
*
Nut
Nut often refers to:
* Nut (fruit), fruit composed of a hard shell and a seed, or a collective noun for dry and edible fruits or seeds
* Nut (hardware), fastener used with a bolt
Nut or Nuts may also refer to:
Arts, entertainment, and media Co ...
*
Rivet nut
*
Screw
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to f ...
*
Screw thread
References
Notes
Bibliography
*.
* Sullivan, Gary & Crawford, Lance
"The Heat Stake Advantage".Plastic Decorating Magazine. January/February 2003 Edition. . (Topeka, KS: Peterson Publications, Inc.). Section: Assembly: pages 11–12, covers Sullivan & Crawford's article.
{{DEFAULTSORT:Threaded Insert
Hardware (mechanical)
Mechanical fasteners