Threaded insert

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TIME-SERT insert TIME-SERT thread insert.gif
TIME-SERT insert

A threaded insert, also known as a threaded bushing, is a fastener element that is inserted into an object to add a threaded hole. [1] 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 or cast threads into a work piece thereby eliminating a machining operation, or simplify changeover from unified to metric threads or vice versa. [2]



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 often ship the parts with threaded inserts and other kinds of knock-down fasteners pre-installed.

People who use sheet metal or sandwich panel or honeycomb sandwich-structured composite often install threaded inserts to spread shear, tension, and torque loads over a larger area of the material. [3]

Captive nut

Captive nuts come in two basic styles. One type, the cage nut or clip-on nut 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 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 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. [4]

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 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. [5] 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 plastic where the metal insert is in contact, and pressure is applied to press it into position. The plastic material typically reforms around the knurled body of the threaded insert to ensure a good retention.

Externally-threaded inserts

A self-tapping insert Taplok Insert.jpg
A self-tapping insert

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. [6] 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.[ citation needed ] 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. [7] [8] [9] Inserts that are self-tapping and lock via friction are more commonly known by the trademarked names Tap-lok or Speedserts.

Helical insert

A helical insert Helicoil plus.jpg
A helical insert

A helical insert is an insert made of coiled wire. The helically formed coils of diamond shaped stainless steel or phosphor bronze 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 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 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 thermoplastics. [10]

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 fit inserts are internally threaded and have a knurled outer diameter. They are pressed into a plain hole with an arbor press. [10]

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. [11]

See also

Related Research Articles

Taps and dies are tools used to create screw threads, which is called threading. Many are cutting tools; others are forming tools. A tap is used to cut or form the female portion of the mating pair. A die is used to cut or form the male portion of the mating pair. The process of cutting or forming threads using a tap is called tapping, whereas the process using a die is called threading.


A grommet is a ring or edge strip inserted into a hole through thin material, typically a sheet of textile fabric, sheet metal or composite of carbon fiber, wood or honeycomb. Grommets are generally flared or collared on each side to keep them in place, and are often made of metal, plastic, or rubber. They may be used to prevent tearing or abrasion of the pierced material or protection from abrasion of the insulation on the wire, cable, line being routed through the penetration, and to cover sharp edges of the piercing, or all of the above.


A fastener or fastening 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 dismantled without damaging the joining components. Welding is an example of creating permanent joints. Steel fasteners are usually made of stainless steel, carbon steel, or alloy steel.

Bolted joint

Bolted joints are one of the most common elements in construction and machine design. They consist of fasteners that capture and join other parts, and are secured with the mating of screw threads.

Self-tapping screw

A self-tapping screw is a screw that can tap its own hole as it is driven into the material. More narrowly, self-tapping is used only to describe a specific type of thread-cutting screw intended to produce a thread in relatively soft material or sheet materials, excluding wood screws. Other specific types of self-tapping screw include self-drilling screws and thread rolling screws.

Knurling Patterning of metal

Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is rolled into the material.


Swaging is a forging process in which the dimensions of an item are altered using dies into which the item is forced. Swaging is usually a cold working process, but also may be hot worked.

Cage nut

A cage nut or caged nut consists of a 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, for example, in the mounting rails of equipment racks. When the wings are released, they hold the nut in position behind the hole. Cage nuts conforming to this description were patented in 1952 and 1953. This design requires insertion tools to install the cage nut into the hole. Newer designs featuring a squeeze-and-release tab allow for tool-less installation.

Piezoelectric motor

A piezoelectric motor or piezo motor is a type of electric motor based on the change in shape of a piezoelectric material when an electric field is applied. Piezoelectric motors use the converse piezoelectric effect of piezoelectric sensors, in which deformation or vibration of the piezoelectric material produces an electric charge. An electrical circuit makes acoustic or ultrasonic vibrations in the piezoelectric material, which produce linear or rotary motion. In one mechanism, the elongation in a single plane makes a series of stretches and position holds, analogous to the way a caterpillar moves.


A countersink is a conical hole cut into a manufactured object, or the cutter used to cut such a hole. A common use is to allow the head of a countersunk bolt, screw or rivet, when placed in the hole, to sit flush with or below the surface of the surrounding material. A countersink may also be used to remove the burr left from a drilling or tapping operation thereby improving the finish of the product and removing any hazardous sharp edges.

Set screw Type of screw

A set screw, also known as a blind screw or a grub screw, is a type of screw generally used to secure an object within or against another object, usually without using a nut. The most common examples are securing a pulley or gear to a shaft. Set screws are usually headless, meaning that the screw is fully threaded and has no head projecting past the thread's major diameter. If a set screw does have a head, the thread will extend all the way to the head. A set screw is almost always driven with an internal-wrenching drive, such as a hex socket (Allen), star (Torx), square socket (Robertson), or a slot. The set screw passes through a threaded hole in the outer object and is tightened against the inner object to prevent it from moving relative to the outer object. It exerts compressional or clamping force through the bottom tip that projects through the hole.

Sex bolt

A sex bolt,, is a type of fastener (nut) that has a barrel-shaped flange and protruding boss that is internally threaded. The bolts sits within the components being fastened, the flange provides the bearing surface. The sex bolt and accompanying machine screw sit flush on either side of the surfaces being fastened. It is normally chosen because of its low profile compared to other nuts. The sex bolt often has a built-in feature, such as a slot, to aid in tightening the fastener. Some sex bolts, more commonly known as "architectural bolts", have knurled barrels to allow one-sided assembly. "Binding posts" are similar to architectural bolts in that they are designed to be assembled from one side, but they have teeth on the flanged surface to keep them fixed.

Rivet nut

A rivet nut, also known as a blind rivet nut, or rivnut, is a one-piece internally threaded and counterbored tubular rivet that can be anchored entirely from one side. It is a kind of threaded insert. There are two types: one is designed to form a bulge on the back side of the panel as a screw is tightened in its threads. The other is similarly drawn in using a screw, but is drawn into the sleeve instead of creating a bulge.

Swage nut

A swage nut or self-clinching nut is a type of nut or threaded insert that is used on sheet metal.

A clip-on nut, also known as a sheet metal nut or a 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.

Screw Type of fastener characterized by a thread wrapped around a cylinder core

A screw and a bolt are similar types of fastener typically made of metal, and characterized by a helical ridge, known as a male thread. Screws and bolts are used to fasten materials by the engagement of the screw thread with a similar female thread in the matching part.

Nut (hardware)

A nut is a type of fastener with a threaded hole. Nuts are almost always used in conjunction with a mating bolt to fasten multiple parts together. The two partners are kept together by a combination of their threads' friction, a slight stretching of the bolt, and compression of the parts to be held together.

Threading is the process of creating a screw thread. More screw threads are produced each year than any other machine element. There are many methods of generating threads, including subtractive methods ; deformative or transformative methods ; additive methods ; or combinations thereof.

Inserts are pins, bolts, screws, joints and other structures that are used to transfer localized loads to a composite panel or to join two composite panels together. Metallic inserts are commonly used in the aerospace and marine industries to attach objects to sandwich composite panels.

Screw extractor

A screw extractor is a tool for removing broken or seized screws. There are two types: one has a spiral flute structure, commonly called an easy out after the trademarked name EZ-Out; the other has a straight flute structure. Screw extractors are intentionally made of hard, brittle steel, and, if too much torque is applied, can break off inside the screw that is being removed. Since the extractor is an extremely hard material, and a typical home shop drill bit will not be able to drill into it, a larger element of difficulty is added to the original screw extraction project. One way to avoid this added difficulty is to drill a hole completely through the screw. Thus, if the fastener breaks, a punch can be used to drive out the easy out from the screw, via the back, or end, of the fastener.



  1. "Repairing damaged threads: Types of thread repair inserts |". Retrieved 2017-09-30.
  2. "Newman Tools Inc". Retrieved 2012-02-29.
  3. "Delron Inserts for Honeycomb and Sandwich Panels" (pdf). Retrieved 2013-06-03.
  4. McMaster-Carr, p. 3150.
  5. Sullivan, G. & Crawford, L. "The Heat Stake Advantage" (PDF). Plastic Decorating Magazine (January / February 2003). Archived from the original (PDF) on 2015-06-10. Retrieved 2013-04-26.
  6. "Inserts For Metal". E-Z Lok. E-Z Lok.
  7. McMaster-Carr, p. 3204.
  8. McMaster-Carr, p. 3206.
  9. McMaster-Carr, p. 3207.
  10. 1 2 McMaster-Carr, p. 3209.
  11. "Composite Potted-In Inserts". Marketing Masters. Retrieved 25 June 2020.