Helicoil Inserts in Aluminum: When Are They Worth It?

Helicoil inserts in aluminum are a common answer when a machined part has to be opened and closed for its whole service life.

Should You Use Helicoils, Keenserts, or Plain Tapped Threads for Screws in Aluminum That Get Removed Often?

For small screws that are assembled and removed many times, a thread insert is usually the safer choice. For a joint that is fastened once, a properly sized tapped hole with enough thread engagement is often enough. Either way the hole gets tapped: a Helicoil goes into a hole tapped with a dedicated STI tap.

An r/AskEngineers user designing an aluminum extrusion heat sink needed blind M2.5 threads that would be assembled and disassembled many times, and asked about Helicoil or Keensert inserts. Replies said Helicoils work well in aluminum for repeated assembly, and that Keenserts hold up better if the fasteners see significant stress. One engineer said their team had moved to Keenserts because Helicoils had been less reliable for them. Another warned that Helicoils can loosen and come out with the screw after repeated over-torquing. These are individual experiences, not test data.

Why inserts help

In a related thread, one reply put it simply: the main advantage of an insert is wear. You also get a little extra strength, because the insert's outer thread into the aluminum is a slightly larger diameter. The same reply said that for a joint fastened once, correct sizing matters more than an insert.

Helicoil vs key-locking insert

• Helical coil (Helicoil). A wire coil installed in a hole tapped with a dedicated STI tap. It doesn't replace tapping; it lines a tapped hole. On tanged versions the tang is broken off and removed after installation, per NASA's process specification for helical coil inserts.
• Key-locking (Keensert style). A solid insert held by keys. Replies favored it where loads are higher, and one said Keenserts use standard taps. Check the tap callout for the insert series you pick.

Designing Helicoil inserts in aluminum

• Size the length from the catalog. One reply suggested two-diameter-long inserts in aluminum if there's room, and checking that the screw passes all the way through the insert. The Heli-Coil catalog lists five lengths, from 1 to 3 times the nominal diameter.
• Allow for the tang in blind holes. Replies noted that getting the tang out of a deep blind hole can be tricky. The same catalog lists tangless inserts (metric M2.5 to M6), which it says eliminate tang break-off and retrieval.
• Check the wall around the larger tapped hole.
• Call out the insert (type, thread, and length) on the drawing, not just the thread.

Related: tap drill percentage in titanium vs mild steel and roll taps vs cut taps.

At DigiForge

We machine Aluminum 6061 and Aluminum 7075, among other materials, with ISO 2768-m as the listed standard tolerance. Put the insert callout on the drawing so it's reviewed with the rest of the part. If you need us to supply and install the inserts, ask us when you quote.