Diameter 1.75 in - 44.5 mm
 
The hole for the threaded adapter was drilled off-center, but it is plumb. The off-center hole WILL NOT be noticeable when the shift knob is installed. The shift knob will still function as expected and the issue is only a cosmetic imperfection.
 
This shift knob has the high gloss mirror finish that we normally use. It is moisture and uv resistant, but like all of our shift knobs, we recommend keeping the shift knob covered when the car is parked outside for long periods of time (30 mins or longer).