NMO Mounting Hole Questions - Totally new at this, but getting totally interested...

[Dtax]

Hi all - very new at this, so appreciate any advice and patience. I also tried a quick search in forums before asking, but nothing jumping off the page. 

Also sorry for the long post! - could be a first timer thing.... 

Question on NMO mounting. I am getting into GMRS via offroading, also new to me. I am making the switch from a hand held to an onboard MXT575. I want to mount a Midland ghost antenna to a bracket on my ditch light bracket up by the windshield / a pillar of my truck. 

Questions: 

I have a ditch light extension bracket that has a 3/4" hole. Midland mounts use a 5/8" hole (my kit came with a different kind of bracket I won't use, but using it as a reference).

The short question is, does it matter? 

The reason for asking is because the Midland antenna wire / mount has a plastic bushing that steps from a 3/4" OD to a 5/8" OD.

Like this: 

As a result when inserted in a bracket with a 5/8" hole, the 3/4 " part of the bushing sits above the bracket. Whereas, if used in a 3/4" hole, obviously, the bushing rests flush in the hole. 

5/8" hole pics  

 

Here a pics of the 3/4" hole 

So I am wondering if that raised collar of plastic is needed to ensure proper insulation or isolation from the bracket on which it is mounted. 

I see the O-ring on the bottom of the brass mount, but that to me seems more like weather proofing than insulation. However, even looking at how it all mounts when fully assembled, it is hard for me to even figure out what matters or not. 

5/8" hole 

3/4" hole 

I have other questions about the effectiveness of this mounting location, but I will take one step at a time. 

Any help is super appreciated and thank you all for hosting a forum like this. Again, apologies for any newbie effect. 

 

[BoxCar]

Having the collar above the hole allows the antenna to make a better water-resistant seal for the connection.

[Dtax]

Thank you - appreciate the reply! 

I can see that. I may look into some kind of 5/8 washer to put under the collar. You think that would create any performance issues? 

[gortex2]

Is the top nut flat on the bottom ? you didn't show that. You need the teeth on the bottom of the mount up against the steel bracket as well as the top nut. 

 

 

[Dtax]

1 hour ago, gortex2 said:

Is the top nut flat on the bottom ? you didn't show that. You need the teeth on the bottom of the mount up against the steel bracket as well as the top nut. 

 

 

My apologies, I am wondering what you mean by the top nut. 

the only male side on the top of the bracket is the wide brass ring with threads on the outside that the antenna will mount to. 

The last picture I showed is all the parts assembled with the teeth nut on the bottom of the bracket, but noting like that on top. 

these are all the arts that came with my shipment from Midland and nothing indicates that I am missing parts from what i can see on their website. 

any further advice is appreciated. 

thank you 

[gortex2]

The top brass nut is what I meant. If its not recessed on the bottom to accept the plastic ring I'm not sure what the spacer is for. A normal 3/8" mount is pictured below and you can see the recess in the brass nut.

 

A standard NMO wouldl ook like this  

 

[Dtax]

@gortex2 thank you - appreciate the insights. Have a good weekend.