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Repair engineering problems – HELICOIL® TWINSERT

The HELICOIL® TWINSERT system consists of two interlocking HELICOIL® inserts, an outer coil installed into an oversize tapped hole which then has a smaller inner coil fitted inside to give a standard female thread.


Is the tapped hole badly damaged? Has the thread been cut too large?


For these cases the HELICOIL® TWINSERT is the ideal repair element.

HELICOIL® TWINSERT consists of two HELICOIL® thread inserts. The external element is a HELICOIL® free running. For the internal insert you can choose between HELICOIL® free running and HELICOIL® screwlock.


free running


Every thread of the thread insert with precision formed, rhombic profile is free running. The result is an internal thread true to gauge that can be used on both sides.

Our seal of quality, a rhombic imprint at the end of the last thread, unmistakably identifies each Böllhoff HELICOIL® free running as an original Böllhoff product.


HELICOIL® screwlock

The HELICOIL® screwlock bears the same benefits regarding threads as the HELICOIL® free running.

In addition, an integrated screw-locking area serves as a screw lock.

Locking of the screw is achieved by one or several polygonal-shaped threads that clamp the flanks of the screwed-in screw. The result is an elastically resilient frictional locking.

The HELICOIL® screwlock can be recognised thanks to its red colour.
The HELICOIL® screwlock inserts can only be used with screws of property class 8.8 or higher.


HELICOIL® TWINSERT offer a great degree of correction to oversize tapping errors because of the larger diameter that results from installing one insert inside another. This larger diameter allows repair of stripped threaded holes as well as off centre standard tapped holes. Hiles tapped with incorrect diameter or incorrect pitch can also be repaired.

HELICOIL® TWINSERT assembly steps


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