Antenna threaded shaft length

[domeboys]

I recently tried to replace the hood-mounted three-mast antenna that had been broken at the base on my 1970 Challenger. However an inexpensive repro that is said to be correct for the car has a threaded shaft that is a half-inch longer than the one that was previously installed. As a result, the replacement will not screw all the way in (and in fact snapped off again because I did not notice the difference in length until it was too late). Does anyone know if the correct threaded shaft length for this car is 3/4" or 1-1/4"? (see photos)

Would I better off trying to find a 3/4" or grind down a 1-1/4" one to 3/4"?

The fender was replaced during restoration with an original fender from another car, but the prior antenna, base and cable were re-used. However, I cannot guarantee it is original and not replaced at some point since 1970.

I would appreciate anyone's advice. Thank you.

 

[floyd]

Here’s an NOS antenna that is 1.25”. Also, I measured the hole depth on the antenna mounts on my cars. One’s original and one is NOS. Both are 1.5” deep. I wonder if you had some cross threading or a piece broken off in there before you tried to install?

 

[EW1BH27]

Here's a some pics for you, Unfortunately I didn't measure the length of the telescoping one's stud. The last one is just "deja vu".

 

[domeboys]

Thank you for the replies and photos. There is no evidence of cross-threading. The stud that was in there previously does not look as if it was snapped at the bottom but I cannot rule out a broken off piece of a prior stud still being down there, getting in the way.

It is interesting that the solid mast stud is shorter, like mine, but my car clearly had the telescoping antenna.

I guess I get another and shorten it to 3/4"...