thanks for all the help. I drilled a hole but the threaded part was not long enough to screw the nut on. I tried several ways to squeeze the center support so I could get the nut started.
Finally I counter sunk the end closes to the mirror to get a few more screw threads to allow me to screw on the nut.
Went for a drive and I love the mirror. A lot more visibility. [Linked Image]