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Helicoil Callout & NASM spec

Helicoil Callout & NASM spec

Helicoil Callout & NASM spec

Hi, our customer returned parts due to bad helicoil threads. There were several issues: some were tanged, locking and not free-running, over-installed (way too deep), damaged (feels like our contract manufacturer just had a bucket of random helicoils and tried to force install damaged threads).

The drawing has this callout:

4X ⌀ .120 THRU

Was the free-running callout was essential, did the note need to specify a particular install depth (NASM spec says .25p-.50p below the surface for non-countersunk holes.), and was a BOM for the helicoil necessary or the installation callout sufficient? Those issues were ambiguous for the drawing note, but I think the other issues are very much the shop at fault.

RE: Helicoil Callout & NASM spec

Presuming the minor diameter was correct, that's the sort of callout I used for nearly 30 years and never had a problem with helicoils unless locking compound was used - then it was 50/50 if the helicoil bonded to the screw or the hole.

There are locking helicoils, which are binding. Perhaps those were in the bucket as well.

Your manufacturer also had a bucket of random workers who were never trained to install them.

I don't have a copy of NASM33537, but that certainly has the required information - it's possible and very likely the manufacturer didn't want to pay for a copy of it. IHS sells copies for $60USD.

RE: Helicoil Callout & NASM spec


My SolidWorks process is to attach the thread insert to my model as a part. I have a bill of materials on the drawing calling up the insert. I have a note stating that thread inserts are to be installed as per the manufacturer's instructions. Tap drill diameters are not inspectable. I take it this specification is outside your control.

The CAD model I have set up calls up the Helicoil part number of a free-running insert. I have a note on the drawing that states that the vendor may substitude an equivalent thread insert. Generally, it is not possible to indentify the manufacturer and part number of an installed insert. If you absolutely need inspectability, specify pull-out strength.

Locking helical inserts generally are coloured a purplish red.


RE: Helicoil Callout & NASM spec

I do same as drawoh.
We have had problems in past with installations. More people don't know how to install them.

Chris, CSWP
ctophers home

RE: Helicoil Callout & NASM spec

Thanks everyone,

I appreciate the input. I feel mostly vindicated. Our manufacturer's problem report included insufficient training.

RE: Helicoil Callout & NASM spec

If getting the NASM standard is a problem, there's an equivalent MS standard that you can access for free.
If the process to install still isn't clear, you can access installation instructions from Stanley/Loctite.
I normally install using the manufacturer's tool kit when I do it myself.
I have included the tool kit part number on installation drawing notes at times.

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