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The use of plastics in the engineering and manufacturing sectors is increasing. Our expansion inserts offer an easy-to-assemble alternative to other types of insert if you’re looking for a solution that provides a strong, reusable thread in plastics that is quick to install.

The brass expansion inserts that Technifast supply have a knurled outer surface designed to offer high pull-out resistance when installed into the host material. Our range offers a choice of headed or parallel inserts, which can simply be pressed into a pre-moulded hole, anchoring the knurled surface into the wall of the hole.

Another feature of our expansion inserts is the two machined slots to allow flexibility as they are inserted into the plastic. The insert will then expand with a radially outward force when the mating screw is installed to ensure a secure fit into the hole.


  • Series 81 (Parallel)
  • Series 82 (Headed)


  • Brass


  • Expansion inserts are hand-placed into a hole of specified size and the action of the screw on final assembly locks the insert into place. 
  • They are ideally suited for use in plastics which are strong enough to resist the expansion of the insert yet flexible enough to allow the knurls to anchor into the material.
  • Series 81 parallel and Series 82 headed inserts are available in brass. We can also supply Series 32 inserts for tapered holes and Series 11 symmetrical ultrasonic inserts.


Nominal Thread Size M3 M3.5 M4 M5 M6 M8
Diameter 'A' 3.96 4.72 5.50 6.32 7.90 9.50
Head Diameter 'H' 5.53 6.35 7.13 7.92 9.52 11.10
Head Thickness 'T' 0.50 0.65 0.81 1.00 1.24 1.24
Length 'L' (mm) 4.72 6.32 7.92 9.42 12.70 12.60
Recommended Hole Size (Min / Max) 4.00 / 4.10 4.80 / 4.90 5.60 / 5.70 6.40 / 6.50 8.00 / 8.10 9.60 / 9.70

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