White knob on transmission mount?

[BCW Austin]

New to this forum. New owner of a 2000 Limited 2 wheel drive automatic with 101k mikes. Gear selector had a lot of movement when I bought it, so I replaced the transmission mount and the movement is gone. What is the white knob at the end of the center bolt through the mount for? There were no instructions and I have searched youtube and this forum for info and found nothing. Thanks in advance.

BCW Austin

 

[orbot]

anyone had info on this, whats the purpose of that middle bolt. and how the f..k you you tighten it.