BNC Thread Size

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Jake Wells
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BNC Thread Size

Post by Jake Wells » Sat Jul 06, 2019 4:52 pm

I'm planning to make a BNC to conflat adapter for different probes I want to use within my chamber. I have a 2.75" conflat blank flange and standard panel mount BNC connectors laying around that I plan to use (https://www.americanradiosupply.com/75- ... c-3194-75/). I cannot seem to find a lot of information about the thread size of the connector. Does anyone know what drill and tap size to use for installing these types of BNC connectors?
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Roberto Ferrari
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Re: BNC Thread Size

Post by Roberto Ferrari » Sat Jul 06, 2019 5:37 pm

Hi Jake

Beware not all BNC are hermetical.
We learned it the hard way...
See Andrew Seltzmann posts related to ion source construction.
Best
Roberto

Jake Wells
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Re: BNC Thread Size

Post by Jake Wells » Sat Jul 06, 2019 7:21 pm

I understand that. Right now I just need to know what tap and die to use.
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John Futter
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Re: BNC Thread Size

Post by John Futter » Sat Jul 06, 2019 8:44 pm

0.5" UNEF the E is for extra fine

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Rich Feldman
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Re: BNC Thread Size

Post by Rich Feldman » Sun Jul 07, 2019 2:05 am

I bet the fine thread, for nut on a bulkhead mount BNC jack, is not covered by general connnector standards.
Any more than the hole spacing for a bulkhead mount BNC with square flange and four small holes. Which ought to be just as vacuum-tightable, eh?

If the ones you have are all the same, and your measurements appear to match a standard screw like what John named, I'd go with that.

It would be different if the thread were part of the connector mating system, as with TNC and HN and SMA connectors.
Here it's more like the thread for mounting a toggle switch or indicator light -- guaranteed to fit the nut that came with it. Often there _is_ a sort of de facto standard, but I would not whine if some BNC scrounged elsewhere is threaded differently.

[edit] The link you provided, for representative picture of a connector, is for 75 ohm style. There's not much freedom for a BNC designer to change the conductor diameters. So as Richard Hull and others have warned, 75 ohm designs tend to have air in place of some of the solid dielectric in regular 50 ohm BNC's. Beware of reduced breakdown voltage.
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John Myers
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Re: BNC Thread Size

Post by John Myers » Sun Jul 07, 2019 5:16 am

BNC threads are generally 3/8-32 (never seen anything else).
3/8-32 seems to be common thread for electronic panel mounts for connector and switches.

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Richard Hull
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Re: BNC Thread Size

Post by Richard Hull » Sun Jul 07, 2019 6:30 am

John and Roberto are correct. I once scored a 6" diameter CF flange with 5 SHVBNC vacuum tight connectors as part of an instrument at a hamfest. I removed them and sold the hole filled flange along with some stainless scrap to the local metal scraper. These connectors are big bucks if you have to buy them. Fused ceramic material is used for insulation as in a normal feed thru.

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