What are Tappex Threaded Inserts?

Tappex threaded inserts, also known as Tappex thread inserts, are precision inserts from British manufacturer Tappex that form a branded part of Accu's threaded inserts range, giving plastic and light alloy parts a durable machine thread. Each is a small metal cylinder with a metric internal thread and an outer form built for its installation method: barbs on Multisert, cutting flutes on Trisert, cutting facets on Trisert-3 and a diamond knurl on HiMould. That outer form anchors the insert against torque and pull-out, so screws can be fitted and removed repeatedly without wearing away the parent material.

Tappex has made thread inserts in Britain since 1956 and its designs suit moulded automotive components, electronic and electrical enclosures, medical device housings and equipment for marine or food processing environments.

How Tappex Threaded Inserts Work.

Each Tappex design locks into the host in a different way. Multisert has an external barb form that can be cold pressed, heat pressed or, in its unheaded and some headed versions, fitted ultrasonically, with heat or ultrasonic installation giving higher pull-out resistance than a cold press. The Tappex Trisert and Trisert-3 are self tapping and cut their own thread into a plain moulded or drilled hole, Trisert through three primary and three secondary cutting flutes and Trisert-3 through three curved cutting facets, both on a solid, unslotted body that resists collapsing in harder materials. HiMould is moulded in: it's pushed onto a plain pin in the tool and the molten plastic flows around its diamond knurl and grips it as it sets.

Consider a 30% glass-filled nylon housing for an automotive electronic control unit, closed with M4 screws that come out every time the unit is serviced. A brass Trisert installed after moulding gives each screw a free-running metal thread, so the housing survives repeated servicing without the bosses stripping. Move the same housing into a marine engine bay and a Trisert-3 in Stainless Steel - Marine (A4) fits the same size hole, so the corrosion resistance improves without redesigning the boss.

Materials Tappex Threaded Inserts Are Made From

Tappex threaded inserts are made from engineering metals matched to the host material and the environment the joint will see:

• Brass: Multisert, Trisert and HiMould use CW614N free-cutting brass, which machines cleanly into fine barbs, flutes and knurls, conducts heat well during heat and ultrasonic installation and withstands corrosion in most environments without further treatment.
• Stainless Steel - (303): Trisert-3 in a free-machining austenitic grade, combining good wear resistance with mechanical strength for harder engineering plastics and light alloys.
• Stainless Steel - Marine (A4): Trisert-3 in molybdenum-bearing stainless steel, which Tappex positions for marine, chemical and food processing environments.
• Titanium - (Grade 5): Trisert-3 in Ti-6Al-4V, a high strength, corrosion resistant alloy at little more than half the density of steel.

Three finishes are offered:

• Natural: The self-colour finish on every brass Multisert, Trisert and HiMould insert.
• Clear Passivated: Used on the stainless steel and titanium Trisert-3 inserts to support their protective oxide layer.
• Zinc Nickel plated and Trivalent Passivated: Applied to case-hardened steel Trisert-3 inserts, giving sacrificial corrosion protection without hexavalent chromium.

Sizes & Types of Tappex Threaded Inserts Available

Accu's Tappex range is available in a variety of sizes and designs for both post-mould and mould-in installation:

• Insert Type: Multisert, Trisert, Trisert-3 and HiMould.
• Installation Method: Cold Press / Heat Press, Cold Press / Heat Press / Ultrasonic Press, Self Tapping and During Moulding.
• For Use With: Thermoplastics, or Wood, Plastic & Non-Ferrous Metal (Requires Pilot Hole).
• Internal Thread Size: M1.6 (1.6 mm) to M6 (6 mm).
• Length (L): 1.35 mm to 14.5 mm.
• Outer Diameter (OD): 2.65 mm to 10.05 mm.
• Recommended Hole Size (HS): 2.3 mm to 9.55 mm.
• Flange Diameter (FD): 3.2 mm to 12.7 mm.

The whole range stops at M6. M1.6 is a single flanged Multisert, while M2 and M2.5 come in brass Multisert, Trisert and HiMould only. Trisert-3 runs from M3 to M6 in flanged form, in a shorter and a longer length series, except titanium at M3, which comes in the longer length only. Flanged Multisert versions are not all suited to ultrasonic installation, so check the Installation Method for each part. HiMould inserts are unflanged and come in open-ended and blind-ended versions, some with a counterbore; as they are moulded in, they list an Installation Pin Length (PL) and Installation Pin Diameter (PD) rather than a hole size.

For threads above M6, Stainless Steel - (A2) Self Tapping inserts in Accu's Threaded Screw Inserts range run up to M20. Where a less specialist and lower cost insert will do the job, Accu's own brass Fix range in Brass Threaded Inserts is the alternative, with heat set, ultrasonic, press-in and moulded-in designs.

FAQ

Q: What is the difference between Trisert and Trisert-3?

A: Both are Tappex self tapping inserts, built for different hosts. Trisert inserts are brass, run from M2 to M6 in flanged and unflanged versions and use three primary and three secondary cutting flutes to thread into thermoplastics. Trisert-3 comes in Stainless Steel - (303), Stainless Steel - Marine (A4), Titanium - (Grade 5) and case-hardened steel from M3 to M6, always flanged, with three curved cutting facets designed for harder hosts, including light alloys such as aluminium and magnesium.

Q: How is a Tappex HiMould insert held in the mould tool?

A: A Tappex HiMould is pushed straight onto a plain pin in the tool rather than screwed onto a threaded one and a slight interference between the pin and the insert's thread holds it in place until the plastic flows around its diamond knurl. Each HiMould in Accu's range lists the Installation Pin Length (PL) and Installation Pin Diameter (PD) it needs, which saves time threading inserts onto pins between shots.

Q: Can Tappex Multisert inserts be pressed in cold?

A: Yes, every Tappex Multisert in the range lists cold press and heat press installation. The unheaded and some headed versions can also be fitted ultrasonically. Cold pressing suits flexible thermoplastics and needs no heating equipment, while heat or ultrasonic installation beds the barbs further into the plastic for higher pull-out resistance.

Q: Can Tappex inserts be used in metal?

A: Trisert-3 can. It's specified for wood, plastic and non-ferrous metal, with Tappex designed for light alloys such as aluminium and magnesium. Brass Multisert, Trisert and HiMould ranges are specified for thermoplastics. Tappex's published hole sizes for alloys are slightly larger than for plastics, so confirm the hole for the host material before drilling.

Q: What hole size do Tappex threaded inserts need?

A: Each insert lists its Recommended Hole Size (HS) in the tech spec. The smallest is 2.3 mm to 2.5 mm for the M1.6 Multisert and the largest is 9.55 mm for an M6 Multisert. Trisert and Trisert-3 share the same figures, from 4.1 mm to 4.4 mm at M3 rising to 8 mm to 8.4 mm at M6, while HiMould needs no hole because it's moulded in. Tappex gives these as reference sizes, so trial them in the actual part before committing production tooling.

Bespoke Tappex Threaded Inserts Manufacture.

High precision, bespoke manufacture of Tappex Threaded Inserts to customer specification. State of the art facilities specialising in both small batch prototyping and large scale manufacture.