Ah ha!  I thought it looked vaguely familiar.  Okay, after a lot of going down various rabbit holes, I pulled out a Type N male connector that you had asked about earlier, and the thread is a 5/16-24 - very possibly the same as on your ZB-1.  You can check it by laying a pocket scale alongside the thread and counting the number of threads in 1/4", then multiply by 4.  (I did it that way for years, but I just use a thread gauge these days.)  The only problem with the Type N is that pesky 5/16"OD shield around the 1/16" center pin.  If you could machine that 5/16" diameter shield off back to the bottom, I'll bet it the modified N connector would fit just fine.  If you or a friend have a lathe, this is dirt simple.

Sorry to take so long, but that transition period at the beginning of WWII is nasty from a parts detail standpoint.  The original ZB and ZB-1 RF connectors were the Navy CW-49137 or CSX-49137 (Western Electric and Selector Manufacturing Corporation - good luck finding any of those).  There was a period when the transition connectors on yours and the one I donated to the Smithsonian below were used before that final SO-239 type was chosen for the ZB-2 and ZB-3.

   73,
- Mike
 

On 8/24/2023 10:08 PM, MARK DORNEY wrote:

The thread on the shell is different. Thread on the ZB-1 is finer. The ID of the shell is correct, but the threads aren’t.

Mark D. 
WW2RDO

On Aug 24, 2023, at 7:22 PM, Michael Hanz <[email protected]> wrote:

I would try the shell of the 259 first.  Looks to be a finer thread, though the NASM photo is indistinct.  The PL-259 was the replacement for the one in the ZB-1, but I think the pin may be too large.  It may be one of the connectors that were meant for shielded microphone wire.  I don't have time to research it until tomorrow.

On 8/24/2023 7:10 PM, MARK DORNEY via MRCA wrote:
“N” connectors?

On Aug 24, 2023, at 5:28 PM, MARK DORNEY <[email protected]> wrote:

This is a ZB-1 Homing device.

https://collections.si.edu/search/detail/edanmdm:nasm_A20060110000

It has the same two coax connectors on the back as the ZB-1 that I have, so I’m thinking they are original. What do you even call this type of coax connector, and where can I find two?  I would like to use the ZB-1 with an ARB Receiver.

Mark D.
WW2RDO

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Michael Hanz - KC4TOS