Have you made the decision to drill a hole in your car or truck. You should know this information ...
NMO Mounts of 3/4" hole size are designed to mount from OUTSIDE the body. You will attach the coax and feed the two ears on the mount through the hole. The larger mounting ring will thread on and sandwich the body panel between the ears and the ring. Do not make the hole size larger than 3/4" (do not use a 3/4" conduit hole saw - it will be too large). MEASURE YOUR SAW TO MAKE SURE IT IS NOT LARGER THAN 3/4" ! If you use a step bit, be careful the bit does not extend too far into the vehicle and catch the head liner. A antenna hole saw is designed to do this correctly.
We suggest this YouTube Video for more information:
https://www.youtube.com/watch?v=9eJcC1mNLGc