Do you know of any models that use M8x1.0 valve adjustment screws?

[hotponyshoes]

Is that a recognised and documented manufacturer procedure?

At first glance it sounds dodgy: the inside of the bigger insert will be its nominal thread size (e.g. M8 x 1). The outside of the smaller insert will be the STI thread size for its internal thread size. AFAIK, STI thread dimensions are not the same as ISO metric dimensions. If it were so, you would not have to buy a special STI tap - you could just use the first or second next size bigger same pitch tap.

Yes, they are called twinserts
(Designed like that, not one normal insert screwed into another one)

 

[hotponyshoes]

I've looked at the Timesert inserts. The thread on the outside of the insert is the same pitch as the thread on the inside. So presumably I can still fit them on the rockers I've tapped to a larger size.

The Timesert website is down so I can't find the correct tap size for an M7x1.0 hole.

7.2 I think?

 

[rcx132]

7.2 I think?

If the inside of the insert is M7 plus the wall thickness of the insert, the tapped hole would need to be a lot bigger than 7.2mm?

 

[hotponyshoes]

If the inside of the insert is M7 plus the wall thickness of the insert, the tapped hole would need to be a lot bigger than 7.2mm?

Sorry, didn't read you properly, 7.2 is the drill size!

 

[hotponyshoes]

Tap size for a m7 helicoil would be about 8.4/8.5mm.
I think timeserts are pretty close to the same

 

[Seadog]

The pilot for a helicoil is the nominal thread diameter plus a tiny bit.

 

[Agroshield]

Designed like that, not one normal insert screwed into another one

OK, thanks. I misread the original as applying to standard inserts.

https://www.stanleyengineeredfastening.com/-/media/Web/SEF/Resources/Docs/Heli-Coil/Oversize-Twinsert-HC943-rev4.pdf

...the tapped hole would need to be a lot bigger than 7.2mm

I think Table VIII here has it (8.42mm):

Helicoil tap chart, helicoil tapping chart , helicoil tap size, helicoil tapping size, helicoil

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www.noblefix.com

 

[rcx132]

Ah sorry got confused, 7.2 may be the drill size which then taps out to something bigger.