A Complete Guide to Threaded Inserts

Threaded inserts are metal cylinders with internal or external threads running down their entire length. They are inserted into holes which have been drilled into walls or other materials like metal, wood, or plastic. Their function is to enable the insertion of screws or bolts and make it a relatively straightforward process to remove them for later reuse. They are efficient fasteners and are also used to reinforce or repair existing threads. Once inserted, inserts grip firmly.

These products have several alternative names, including:

• Thread inserts
• Thread bushings
• Threaded sleeve inserts
• Insert nut fixings
• Threaded fasteners
• Screw thread inserts

To install a threaded insert, you will need a drill and a matching installation tool, also known as an install tap. The latter are usually specific to the insert manufacturer. Alternatively, a matching threaded screw or tap bolt can be used to drive the insert into place. Tap bolts, also known as cap screws, are used for drilling directly into hard or soft materials.

Here’s how to install a threaded insert using a drill. The packaging should indicate the required depth of the drill hole. Typically, this will be 8.5-9mm.

1. Prepare your drill, ideally applying a depth stop attachment to prevent the drill from entering the piece of material to too great a depth - and then drill the hole
2. Attach your installation tool or the bolt to the insert thread and then drive the insert into place. An impact driver can be useful here
3. If applying a threaded insert to wood, you may wish to add glue for additional reinforcement

Threaded inserts are sometimes classed as ‘thread-in’ and ‘press-in’, meaning they are either screwed into place or pressed into place.

So, what are threaded inserts used for? Once inserted into a suitably sized hole, they allow the further insertion of screws and bolts, giving them an important role in the toolkits of builders, carpenters, and engineers.

Threaded inserts serve several functions, for example:

• Extending the working life of a drilled hole by minimising wear and tear. Bolts and screws can be removed and reinserted into threaded inserts multiple times without damaging or weakening the existing hole
• Repairing holes which have been stripped or become worn down. So-called thread repair inserts have a greater diameter than the hole into which they have been inserted, thereby compressing the space for a tight hold
• Providing a firm hold in softer material
• Reinforcing screws or bolts in material that is likely to come under strain
• Adding protruding threads to material that would otherwise be too thin
• Simplifying the changeover from one type of thread to another

Threaded applications include:

Because metals like aluminium and steel are harder than wood, thread inserts for metal feature external as well as internal threading to make insertion and removal easier. The outer threads on the metal insert are matched to the existing threading within the hole. They are commonly used in sheet metal.

Timber, hardwood, and plywood can be used with threaded inserts. Both press-in and thread-in inserts can be used. Adhesive is commonly added too.

Threaded inserts for plastics differ according to the characteristics of the material.

Thermoplastic materials are heat-sensitive and as a result, inserts are applied via the application of high temperatures. Once the insert has reached a specific temperature, it is pressed onto the plastic. The latter then melts around the insert before cooling.

By contrast, thermoset plastics are tougher and can be drilled like metal or wood.

Threaded inserts for rubber are not as common as those for wood and metal but when used they can be applied via simple insertion or by placing them into a mould. Heated rubber is then injected where it will harden into place, encasing the insert.

Industry applications for threaded inserts include many fields where parts need to be joined together or fastened securely. Some examples include:

• Building and construction
• Carpentry and woodworking
• Manufacturing and assembly
• Electrical engineering
• Aerospace and automotive engineering
• Industrial engineering and prototyping