Bulkhead hole diameter

[Steve Bryant]

Hi all. My firewall  / bulkhead does not have the hole drilled for the vacuum pipe to go through. Anyone know the proper diameter the hole should be WITHOUT the grommet in it?
Thanks,
Stephen

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[Duncan Grimmond]

Measure the pipe for the right size of grommet and drill a hole to match the grommet?

[Steve Bryant]

Duncan, there is no pipe at present, so was wondering what the original factory diameter was.
Thanks,
Stephen

[Howard Wright]

Hi Steve

The pipe on my car is about 1/4” (it’s squishy rubber so difficult to measure exactly). It is reproduction bought from one of our Cherished suppliers.

Hope that helps 

Cheers

Howard

[Tony Griffiths]

As grommets now all seem to be metric you'd be better off - as others have said - finding some that look to be correct and drilling according to the dimensions of the chosen one (I'd recommend experimenting first on a piece of suitable scrap metal sheet). BTW, the hole would originally have used not a rubber grommet, but one of the rather lovely, two-part, screw-together, nickel-plated metal type. Very similar ones can still be obtained with a search on eBay turning up more than one supplier. Unfortunately, the gap between the two halves of these is greater than the thickness of the bulkhead metal - hence they either need turning down (tricky) or a small washer found or made (very tricky) to compensate.

[Steve Bryant]

Thanks Tony. From what I can see and extrapolate from photos the hole would appear to be 1/2" diameter. I'll turn something up on the lathe to do the job.
Stephen

[Parazine]

I made some up during lockdown for the Top Hat restoration:


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[Chris Garner]

Steve. I think you'll find the diameter is 7/16". I can let you have a brass grommet FOC if it helps.
Parazine. I had a batch made some time back but mine were not as long as yours and closer to the original pattern. I didn't take the risk to Ni plate as I worried about the threads and whether the two halves would screw together after the plate.

[Steve Bryant]

Hi Chris, thanks for the information and your generous offer.  I'll go with 7/16" and open it up to 1/2" if need be. I need to turn up a batch of brass grommets anyway for the wiring when the time comes.
Cheers,
Stephen