Thread size for Humvee antenna base?

[signsup]

Have several two piece whip antennas for the Humvee era vehicles and several spring bases and mounts. All are the same size thread and match up perfectly. I needed one moure base and picked one up in a estate auction parts lot. Mounted it to my mount M998 and it bolts up perfectly, but my antenna sections will not thread on. This spring base is a larger thread size than all my other bases and antenna sections.
I either need to swap out for the correct base. Purchase a smaller thread base, or try to cobble up something that will thread on the base and reduce to the smaller thread size I need.
Are there two main thread diameters? What size am I looking for to match the smaller of the two. And, what is the thread size and pitch of the larger of the two so I can try and reduce it. These are all display antennas and non functional.

Thanks in advance.

 

[juanprado]

You need to post the pics of the base data plates or pics might help.
Most hmmwv have as3900 mounts but you can have older or newer harris models?

 

[signsup]

The first pic is the smaller of the two threads. The second pic is of the larger thread. Hope the numbers are readable.

 

[signsup]

So, with a lot of trial error, here is what I have. It appears that the 3900 base is the larger thread and most of my bases and antennas are of this model. The NOS antenna base and antenna mast I just received is a 6707 and is a small diameter thread. So, I don't need any adapters as I have masts for all my mounts. Hope this helps someone else down the road.
As an aside, one of my antenna mast lower sections is about 12" shorter than all my others, so I will mount that on the sponson on my slant back and that should even out the antenna lengths between the rear tub antenna mount and the sponson mount.

 

[signsup]

Oooops, spoke too soone. After I moved all my mounts and bases between my two Humvees, one a slant back and one a soft top, I still come up a antenna wip lower section short. I have several of the small thread 6707 mast sections, but need one larger 3900 lower section. If anyone has one available wants to trade or sell, I need one to complete my two vehicles. Thank you.