This was one of the reasons Helicoil inserts were used on aluminium and particularly so on castings, I would consider it but you will need to purchase the necessary taps and insert tools.

Inserts are common is aircraft, military and frequently inspected machinery uses for that very reason. Way back I read an article in one of the trade magazines suggesting that inserts were desirable for smaller threads if more than 10 removals were anticipated in the product lifetime and should be mandatory if more than 20 were expected. The article was technical advice by one of the insert suppliers so obviously some advertising licence involved.

Thread size is clearly important. 3 mm, small BA ad similar are definitely on the risky side if regular unskilled removal is likely. 1/4 Whitworth and up I’d consider pretty safe in a decently hard alloy for lighter loads such as holding a cover against a gasket. For heavier loadings maybe not so much.

One major advantage with inserts is the ability to use a finer thread giving more grip in a relatively thin part. So thread depths similar to a standard nut become safe. Coarse threads, like Whitworth / UNC are reckoned to be less stressful on the part but realistically you need rather more depth than a standard nut. I like double nut depth for 1/4″ Whitworth in alloy. Removing the first thread or two to give a bit of plain bore lead in and protect the opening thread from technical damage is a great help when it comes to clean insertion too.

As ever its a judgement thing.

Clive

On 14 August 2026 at 10:36 John Haine Said:

I think Jason has it right – studs much the best option.  Unless they have to be super strong, cut from suitable size stainless studding (clue is in the name), and finish off external en to look nice. Stainless nuts and washers, loctite the studs into the aluminium body.

Or even acorn nuts for appearance, etc.

Our later marine engines had Aluminium components which, from time to time, needed to be separated.

The parent component was helicoiled.

The helicoil will be say 7 x 1 for a M6 bolt, (9 x 1.25 for M8) so will be stronger in the aluminium than the smaller thread would be.

For longevity, helicoil would be ny advice

Howard

On 14 August 2026 at 12:01 Adrian R2 Said:

If we consider something commercial such as a manifold stud on a lawnmower engine it will typically use a stud with a coarse thread into the base casting, a plain section for locating the attached piece and then a fine thread for a nut. The stud is fitted once into the base, access is gained by removing the nut only.

If you can find a suitable sized stud off the shelf then likely easier than inserts.

The only snag with the stud system on machine parts subject to high heat and vibration is if one day the torque required to undo the nut exceeds the torque required to cause the stud to turn.

I’ve met this problem more than once on Honda recoil starter covers which couldn’t be removed to replace a broken pull cord or recoil spring because one or more studs going into the engine block were turning in their seats before the nut could be cracked loose. It then becomes a hacksaw/nut splitter job.

You have given no idea as to size or thread depth + numbers. I have worked on the LARC XV for 27 years. This is an American military amphibious vehicle working in salt water with an alumimium hull. The threads are helicoiled and though built in 1967 seldom give trouble when dis assembled. The bolts are stainless.  This would be my choice.

A helicoil kit is not expensive and if reliability is the criteria then it matters little as to cost.   Noel.