Yepp and I think that's what's giving me so much trouble trying to rotate the head since it snapped off. Trying to drill it out right now....hoping not to do to much damage to anything else...I just looked at my mill. I have three large bolts, not two. (Obviously have not trammed my mill in a while. ) I have a bolt located on each side and one on the bottom of the circular mounting plate. It does not have the smaller bolt you circled. If I had to guess, I would guess that the smaller bolt you have is a binding bolt. Does not seem that useful to me.