I agree with Curt. I only researched Austin Spectra antenna, I didnt care to research NMO mount. I purchased NMO hole mount from Scannermaster and have same problem. Here's what Curt said: "The problem is that the center stem is way to long for the thin metal of a roof mount. I tried to use it with an Austin Spectra and was unable to even begin threading the antenna on the NMO mount I had to get some 3/8 " washers and put on the inside of the vehicle before putting thru body hole and attaching NMO base nut. I shouldn't need to make such adjustments or the necessary washers should be included. The stem was ¼” to long to work with the 14 gauge steel of a vehicle roof and I had to use two 1/8” thick washers to make it fit right"
Completely agree with what he said I spent $140 on the antenna and $23 on the mount. I shouldn't have to do anymore adjustments to already overpriced item. The only reason I bought this antenna is because of good reviews.
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NMO mount
April 24, 2012
Reviewer:
Curt
from Santa Cruz, CA United States
This was my first time using a 3/8" NMO as I usually use a 3/4" NMO and have already installed 4 of that size on this vehicle without problem. The problem is that the center stem is way to long for the thin metal of a roof mount. I tried to use it with an Austin Spectra and was unable to even begin threading the antenna on the NMO mount when the spring of the antenna was pressed against the contact. I had to get some 3/8 " washers and put on the inside of the vehicle before putting threw body hole and attaching NMO base nut. I shouldn't need to make such adjustments or the necessary washers should be included. The stem was ¼” to long to work with the 14 gauge steel of a vehicle roof and I had to use two 1/8” thick washers to make it fit right. Next time I will use a ¾” NMO even if I have to order from vendor different than the antenna vendor
NMO mount 
