Victim: 1970 Coupe

Got a weird problem... can't seem to nail it down...

About 20 years ago, I removed the original antenna wire and fixed mast antenna to install a Harada MT-3 power antenna. To do this, I had to remove the drivers seat and the 3 point harness... and pull up the carpeting, plate etc. PITA

This was the result of a rash of vandalism where kids were snapping off antenna's... and also so I could run the antenna down to install a car cover without poking a hole in the cover.

The Harada MT-3 died.

So I bought a Metra 44-PW22 power antenna from Ecklers (reboxed from Paragon).

The old Harada MT-3 cable connection at the antenna is .250 26TPI.
The new Metra cable connection at the antenna is .250 .75mm. (34tpi)
So.... I cannot connect the old MT-3 cable onto the new antenna.

I was told by Metra that I have to run a new cable... they have no adapter.

Question:

What is the industry jargon these connectors are referred to as?... so I can look up information on an adapter.

Been fishing through Newark catalog and using Google but I can't identify these connectors to know what to ask for in an adapter... or even a splice set (cut the ends off both cables and splice the Metra connector onto the MT-3 cable).

I can't even ID the cable type... to do a splice.

Any idea's ? What are these connectors "called" ?
(besides just coax connectors)

I really don't want to rip the interior out again.