Carefull guy's, that washer is needed.
Been there done that.
The washer insulates the shaft as seen in the pic above.
That is what the coax wire is for.
One wire is ground which should be grounded by drilling a hole into your ARB or TJM bumper.
The other wire from the coax is on the ring that goes around the shaft of the antenna, and it must not come into contact with ground.
You can see also that the nut at the very bottom does not contact any ground of the frame or bumper as it is threaded on the shaft, and what keeps it from gounding is the bottom washer.
If any part of that shaft grounds, your SWR goes out the window.
I have a 1.1 or less match on all 40 channels.
Note also in the pic that it says the washers are for insulating.
In other words, they keep the shaft from grounding.