Latest blog post on Tappex self threading thread inserts for metal, plastics, composite materials and wood

Tappex® has acquired, since it was established in 1957, a comprehensive knowledge of the application requirements of Threaded Inserts fastening across global Industries. In recent years, in particular,  our range of self-threading inserts have been progressively developed to include new products necessary to meet the demands of the metals processing industries and more critical customer applications.

Such critical applications include: Castings, machined & sometimes fabricated parts produced from Light metal alloys i.e. Aluminium, Zinc & Magnesium. Our inserts have been extensively trialled and supplied to customers around the world, on land, sea, air & even in space. Our inserts are of the self tapping type installed into either cast or pilot drilled holes to suit customer’s product manufacturing processes.

TRISERT-3 brass inserts


Self Tapping Plated Steel or Stainless Steel Insert. Self Threading / Post mould installation

The Tappex Trisert-3 has three cutting features to provide a balanced cutting action and reduced installation torque. The Trisert-3 is suited for critical applications and is available in two lengths, regular and long, and is based upon the Trisert Reduced Headed design.

Ensat Threaded Screw Inserts


Threaded Screw Inserts

The use of self-tapping thread inserts has significant advantages over pre-tapped holes, moulded-in inserts and wire thread inserts. They eliminate close tolerance holes required for tapping directly into the base material, damaged tools and low productivity resulting from moulded-in inserts and the time consuming process of placing wire thread inserts into pre-tapped holes. The trisert 3 range offers engineers an easy to fit alternative to traditional thread repair products such as helicoils.

To find out more about our inserts please click the link to visit our webite…

Alternatively if you would like some advice or you have a design or application that you’d like to discuss with our applications engineers, please give us a call on 01789 206600, or drop us an e-mail to


Brass Thread Inserts for Plastics

Tappex® has acquired for over 57 years comprehensive knowledge of the application requirements of Threaded Inserts fastening across global Plastics Industries. Our thread inserts have been designed for plastics installations in mind, have been extensively trialled and supplied for more than half a century to customers around the world, on land, sea, air & even in space applications.

Industries on a global basis specify a wide variety of plastics. Tappex thread inserts, both standard products and customer specials have been developed to meet the many different demands of these different plastics. The manner in which they are used dependant upon customer application(s).

In overview, groups of Industry plastics include:

  • Thermoplastics – rigid at room temperatures but soften at elevated temperatures, ultimately melting if of Amorphous structure i.e. ABS, Nylon (depends on grade), PVC & Polycarbonate OR if of a Semi-crystalline structure whilst these do not behave in the same way, they do have a well-defined melting range i.e. PE, PP & PEEK are good examples
  • Thermosets – once formed through molding, for example, they chemically change such that they cannot be physically re-formed /re-shaped, but are characteristically quite robust and stable at elevated temperatures i.e. Automotive ‘under hood’  installations
  • Foams – limited suitability for threaded inserts unless the holes are suitably cored. Tappex can offer a product for certain applications after further consultation and/or testing, where appropriate
  • Elastomers – rarely suitable for threaded inserts although Tappex always prepared to give some technical consultation
  • Composites – and growing in progressive usage, composite materials which may incorporate combinations of plastics, wood based fibres and/or light alloys can be supported by Tappex, after consultation, either with a Thread insert or bespoke fixing solution

For further details please visit our website or talk to our experienced applications engineers on 01789 206600.

self threading insert,

Thread Inserts for plastics – A ten point guide to best design practices

Tappex are British manufacturers of Threaded inserts for plastic, metals and composite materials. Below is a helpful ten point guide for Designers, Engineers, Specifiers and end users alike…

Design engineers who use plastics face increasing problems when trying to specify high performance inserts that will give reliable cost-effective assemblies. Tappex would like to offer ten points to consider when selecting a threaded fastener for use in plastics.

1 The first essential is to understand the intended use of the insert and the mechanical performance specification that it is expected to meet. The mechanical performance of any insert in plastic will depend upon how it interfaces with any mating parts, i.e., is it to be clamped to a mating surface or is it to be unsupported and,therefore, rely on its grip in the plastic to prevent pulling out. Most fastener manufacturers offer a technical service so designers and moulders should not hesitate to seek their advice.

2 A working knowledge of the proposed production process and the type of plastic to be used is very important. In most instances plastic components are produced by a moulding process. There are a number of different processes used – injection, compression, rotary or blow, resin-injected processes for GRP and composites, and vacuum forming which allow an insert to placed into the mould tool before the plastic is introduced. This process is described as mould-in and, in general, gives rise to the strongest mechanical performance of an insert. However, the design of a component does not always allow this so, by positioning core-pins in the mould tool, moulded holes can be produced for one of several post-mould insertion processes. Alternatively, parts can be fabricated from plastic sheet; this usually involves machining holes for a post-mould insert. Use of thermoplastic grades which remelt after moulding or thermoset grades which do not melt is an important consideration when a suitable insert is being selected.

3 Where possible it is advisable to choose an insert design from a manufacturer’s
standard range of parts. Usually, test data covering various materials will be available to support use in a particular application. A further benefit is that standard parts can be obtained in small quantities off-the-shelf for the support of all pre-production requirements. And they will be readily available to meet production requirements at whatever volume, cost effectively.

4 Although the purchase cost of a fastener is very important, designers need to consider the proposed production process in order to evaluate the true ‘in-place’ cost of the fastener, i.e., the sum total of the fastener piece-part cost plus the cost of installing it into the plastic.

5 Consideration of the proposed production volumes also plays a part in deciding whether to mould-in inserts or install them after moulding, either beside the moulding machine or as a separate postmould process at a later date. While processes such as rotary moulding lend themselves to hand-loaded mould-in inserts they can slow the injection moulding process; unless, that is, the production of very large quantities justifies the capital cost of robotics to simultaneously remove the mouldings and load the inserts automatically within the required moulding cycle time.

6 The choice of insert material is worth noting. Brass is the most popular because, although more expensive than steel, it can be machined faster, and it can be recycled economically requiring less energy to process overall. For moulding-in, brass components are less likely to damage the mould tool should they become misplaced during the mould cycle. For most applications the resistance of brass components to corrosion does not require any additional and costly plating finish which, in itself, makes recycling difficult.

7 The choices for post-mould insert design cover press-fit, either cold or with heat or ultrasonics, and self-tapping. Generally, a designer should not choose to press-fit inserts into thermoset material. They are ideally suited to press-cold into softer grades of thermoplastic materials, such as abs and polypropylene, or with heat into harder grades, such as acrylic and nylons, particularly if they are glassfilled or mineral-filled types.

8 Larger sizes of insert can pose problems if they required to be installed with heat. As significantly more power is required to heat them to the defined temperature, after installation the heat takes more time to dissipate and to allow the boundary layer of plastic to cool sufficiently to fix the insert position in the moulding. Therefore, care in the design of fixtures and in the handling of the moulding is important.

9 For many post-mould applications – particularly in all thermoset grades and in harder thermoplastics with glass reinforcement – a self-tapping design of insert provides a cost-effective and reliable solution. For small production volumes it can be a flexible process that does not require expensive dedicated installation equipment. However, for larger volumes installation can be arranged to take place alongside the moulding machine, often by under-utilised labour during the mould cycle period, This will provide significant cost savings over the lengthier heat insertion methods of installation.

10 From a quality standpoint self-tapping inserts, in both male and female threaded forms, provide a monitored production process utilising torque-controlled clutches, and, because the thread is used for the installation, every insert in a finished moulding has to have the correct thread form to have been installed at all.

All options available for a particular application must be considered based on material grade, process capability, and finished performance to specification. A standard part should be used if at all possible. The alternative is to seek out a specialist manufacturer and ask for a quotation for the production of a special part, placing reliance on the experience of its personnel to incorporate the essential features and tolerances relating to the interface with the plastic.

We hope you have found this guide useful. If you have any further queries or need help with identifying an insert to suit your needs, please do give us a call on 01789 206600 or visit our website… You can also follow us on twitter…@tappexltd